This is the first time Manchester United and Arsenal have met in European competition, although the loud splat of pizza on Sir Alex Ferguson after Manchester United ended Arsenal's 49-match unbeaten run at Old Trafford in 2004 did lend the game a slightly continental feel.

For many years now, matches between these two teams have been fuelled largely by acrimony and punctuated by mass brawls, bone-crunching tackles, bare-faced cheating, red and yellow cards, point deductions, pre- and post-match tunnel-bust-ups, snarling, finger-pointing, ostentatious displays of chest-hair and the occasional sublime goal, all played out over the incessant din of Sir Alex Ferguson and Professor Arsene Wenger sniping away in their respective bids to drive each other completely mad.

Here's hoping we get all of the above and more tonight, although the ostentatious displays of chest hair probably wouldn't be missed.

Man Utd (4-3-2-1): Van der Sar, O'Shea, Ferdinand, Vidic, Evra, Fletcher, Carrick, Anderson, Ronaldo, Tevez, Rooney.
Subs: Foster, Berbatov, Giggs, Park, Scholes, Rafael Da Silva, Evans.

Arsenal (4-2-3-1): Almunia, Sagna, Toure, Silvestre, Gibbs, Song Billong, Diaby, Walcott, Fabregas, Nasri, Adebayor.
Subs: Fabianski, Eduardo, Denilson, Ramsey, Djourou, Bendtner, Eboue.

Referee: Claus Bo Larsen (Denmark)

Players facing suspension if they get booked: Evra (MU), Rooney (MU), Diaby (A), Nasri (A), Song (A).

Players facing suspension if they get booked: Evra (MU), Rooney (MU), Diaby (A), Nasri (A), Song (A).

So, no Dimitar Berbatov in the Manchester United side? He must be injured, because I can't think of any other reason why Sir Alex Ferguson would break the habit of a season and pick Carlos Tevez ahead of him for a big match.

Students: "I'm watching this from Galway library and have a big econometrics exam in the morning, so have barred myself from going to the pub till the second half," writes Ciaran Walsh, his ability to read the report being hindered by the traffic cone that's perched on top of his head. "Ferguson only sees Wenger as a "friend" because Arsenal are no longer challenging for the title, I'll bet you a fiver (of my BOI overdraft) that there is fireworks tonight between them! Nothing like a Champions League semi-final to stoke up some good, old fashioned hate!"

How important can this be in the current economic climate? A lot of peopole seem to have done very well for themselves without having too firm a grasp on it.

This from Kevin Wilson: "Might SAF have played Tevez rather than Berbatov because he plans on using Ronaldo up front and Tevez wide, which wouldn't really be an option if he played Berbatov?" he asks, causing me to wonder if he is by any chance related to theguardian.com's resident giant footballing brain, Jonathan Wilson.

Another email from another student: "I'm following the MBM while studying for a Constitutional Law exam tomorrow (about as useful as econometrics here in the good old U.S. of A)," writes Paul Spencer, probably from his ... frat house. "I'm not going to the pub at all today. But after the exam, all bets are off." So we have a lawyer and an economist on board. Are there any students out there reading this with plans to make something useful of their lives?

Not long now: The teams emerge from the dressing room and line up behind the match officials in the tunnel. Chat is kept to a minimum, although Mikael Silvestre gets a few pats on the back and friendly handshakes from some of his former team-mates.

"Believe" read the mosaics at one end of the ground when the punters hold up their red and white cards. Believe what? The teams line up and the Champions League music is played. United are in their usual home strip tonight, Arsenal's players are kitted out in yellow shirts with blue sleeves, blue shorts and yellow socks.

1 min: United set up with Ronaldo on the right wing, Tevez on the left and Rooney up front alone. For Arsenal, Diaby is playing on the right and Nasri in the centre.

1 min: Rooney takes the heads the first shot on goal and brings a brilliant save out of Manuel Almunia. He headed it downwards, the ball skidded off Sagna's head and was goalbound until Almunia scampered across his line, dived and flicked it clear.

2 min: A slip by Kieran Gibbs allows Cristiano Ronaldo to get in behind the Arsenal defence and drill the ball across the face of goal - there's nobody there to poke it home.

3 min: Samir Nasri gets a ticking-off from the referee Claus Bo Laursen for aiming a petulant kick at Anderson, but the yellow card isn't brought out.

5 min: Only five minutes gone and all the signs are that this is going to be a great game of football, with neither side showing any inclination to adopt the rope-a-dope policy employed by the Stamford Bridge Yellowbacks last night.

7 min: In the final third, Ronaldo picks up the ball on the right wing, tries to cut inside but is dispossessed by Alex Song. Throw-in for Arsenal.

8 min: Carrick shows some nifty footbwork in midfield, before playing the ball across the halfway line to Fletcher. He thumps it forward towards Rooney on the edge of the penalty area, but Silvestre intercepts and heads clear.

10 min: Almunia saves easily from a scuffed Ronaldo daisy-cutter. Manchester United are definitely having the better of it at the moment as Arsenal don't seem to have settled yet.

12 min: Out on the left touchline, Rooney picks up a loose ball and attempts to send in a cross towards Tevez. Toure clears.

13 min: In the centre of the park, Anderson rolls the ball back towards Carrick, who immediately drills it straight ahead of him into the penalty area, in the hope that Ronaldo will run on to it. The Portuguese is on the same wavelength as United's quarter-back, but there's too much welly on the ball and Almunia beats him to it.

GOAL! Man Utd 1-0 Arsenal (O'Shea 16) Great strike from the full-back, who is third in a queue of unmarked Manchester United players waiting to capitalise on errant Arsenal marking. With Michael Carrick in possession and the visitors drawn towards him at the near post like flies towards a turd, he attempts a cross from the byline. The ball takes a deflection off Mikael Silvestre and drops kindly for O'Shea, who's facing goal. Without waiting for it to hit the ground, he rifles a diagonal shot into the roof of the net from seven or eight yards, leaving Arsenal's defenders standing with their hands on their hips, glaring at each other.

19 min: Moments before O'Shea scored that goal, Manuel Almunia made an excellent save from Carlos Tevez, getting down low to parry a sweeping six-yard drive from the Argentinian, who was attempting to finish a move begun by Anderson.

23 min: Corner for Manchester United. Vidic lumbers up from the back, but Anderson's inswinger goes wide.

25 min: Cesc Fabregas tries a shot from distance on the fly, but Wayne Rooney is back doing mundane chores, sticks a leg out and does just enough to put the Spaniard off.

26 min: Arsenal win a free-kick in the centre-circle, just inside Manchester United's half. Sagna plays the ball out wide to the right touchline, where Theo Walcott takes possession. He cuts inside, runs across the face of the penalty area and dinks the ball towards Fabregas, who unleashes a low drive. Van Der Sar saves comfortably.

28 min: "Same old Arsenal, always cheating!" chant the home fans, who have come to cheer on a team that numbers Cristiano Ronaldo among its ranks.

29 mins: Another fine save from Manuel Almunia, who scuttles across his goal-line to save a point-blank header by Cristiano Ronaldo from all of three yards out. Tevez was the provider, having curled in a wonderful cross from the inside right flank. Arsenal are struggling badly here.

31 min: Tevez and Almunia collide on the edge of the six-yard box while contesting a 50-50 through-ball from Anderson. It's looks nasty, but isn't, thanks largely to Tevez's attempts to pull out. Oh behave.

34 min: "Barry, I just tuned in to a dodgy internet feed of the TV coverage, but I've turned it off because I can't stand the commentator - he's a rather unpleasant Scot who sounds like Malcolm Tucker on acid ('he just smashed it in, smashed it in')," writes Matthew Cobb. "Who is he?"

He's no Scot, Matthew, he's an Irishman - I'd bet any money on it. I suspect that you have just been accidentally exposed to the cartoon leprechaun that is ESPN's Tommy Smyth.

38 min: Arsenal dominate possession briefly, but do little with it. They're fannying about in the middle of the United half, with six players between them and the goal.

40 mins: Edwin van der Sar hoofs the ball the length of the field in a bid to pick out Wayne Rooney. He doesn't, but the ball is only cleared as far as Carrick, who does. Rooney cuts inside from the left wing and attempts to curl a shot inside the far post. Wide.

42 min: "Funnier than the BBC but a tad slower," writes Steve H, for reasons best known to himself. In idle moments I wonder has it occurred to people such as Steve, who write in to complain about my tardiness, that my updates might arrive more promptly if I didn't have to waste time sifting through their stupid emails?

44 min: Tevez drills a low ball from midfield towards the edge of the Arsenal penalty area. Anderson chases and strokes it a few yards to his right, into the path of Micheal Carrick. Only a well-timed tackle from Silvestre prevents him from stroking the ball past Almunia and putting United two goals up.

Half-time:

Half-time correspondence: "Here's another stupid email for you to read," writes Jon Cummins. "You have no problem posting the link to an article that completely eviscerates a terrible, but entirely harmless commentator. But when a reader offers you a backhanded compliment you attack him. You've been watching Fergie's press conferences, haven't you?"

And another one: "Any chance that when you add hyperlinks to your MBMs that you make them open in another window/tab, and not just direct you away from the Guardian website?" writes Stuart in Argentina. "I've just spent the last God-knows how long trying to get my head round Econometrics, and have consequently missed the first half." No problem Stuart. It's not like I'm busy or anything.

Sending emails isn't actually obligatory, you know. "You seem to use a player's full name sometimes and other times only his surname," writes Ted. "I have studied this in an attempt to discern a pattern and I now realize that it's probably just that you use only the surname when the game is exciting and it has quickened your otherwise languid pulse, causing you to rush out a hurried account of events, discarding first names in your haste. Of course, this means that I can tell when the game is less eventful by simply looking at how many times you use the full name. This has meant that I can now keep track of games by ignoring the content of your updates and looking at the score and quickly scanning your use of names." Jesus wept.

Second half is go: In the half-time interview he's contractually obliged to give to Sky, Alex Ferguson says his team controlled the game for the opening 35 minutes and would be several goals in front if it wasn't for "their goalkeeper".

48 min: Nothing noteworthy to report so far in this half. Move along. There's nothing to see here.

49 min: "Keano! There's only one Keano!" exhort the Manchester United fans, clearly singing the praises of Tottenham's Robb ...oh. Critiano Ronaldo picks himself from the ground wearing his best "wounded" expression, after coming out second best from a challenge from Kolo Toure without getting a free-kick.

51 min: Fletcher and Anderson combine well in midfield before sending Tevez on a sortie into the Arsenal half. He picks out Rooney on the right, but a promising move by United is snuffed out.

52 min: Alexandre Song, who is one yellow card away from a suspension, is lucky to escape a booking for a challenge-from-behind on Carlos Tevez.

54 min: Fletcher plays the ball forward to Anderson, who's playing very deep in Arsenal territory in this half. He tries to skip clear of Diaby, but is dispossessed.

55 min: "If Stuart in Argentina was proficient with computers he would know that all you need to do is right click on the link and select 'open in new window'," writes Sean Kinnear, licking Monster Munch crumbs from his fingers while deciding whether to attend the new Star Trek movie dressed as a Napean (a race of partially empathic humanoids from Napea II) or a Borg (enhanced humanoids native to the Delta Quadrant).

58 min: Arsenal win a throw deep in Manchester United territory and the ballboy risks getting a clip around the ear by dilly-dallying in returning the ball to Bakari Sagna.

60 min: Galloping through the centre, Rooney plays a diagonal ball out to Cristiano Ronaldo on the right, who dinks it back into Rooney's path. With two Arsenal players in front of him, he attempts to tee it up for Anderson, who shoots high and wide from the edge of the penalty area.

63 min: With Anderson playing high up the pitch, Alex Song exploits the gap he's left behind and rampages forward. He curls a ball towards Emmanuel Adebayor, who gets behind Ferdinand, chests it down, swivels and shoots ... wide.

64 min: The camera pans to Theo Walcott, for the benefit of TV viewers who might have been wondering if he'd come out for the second half. He's had a very quiet night.

65 min: Cristiano Ronaldo throws a bona fide tantrum and it's priceless. With his features scrunched up in a petulant scowl, he balls his fists, waves them up and down in the air, stamps his feet and whimpers like a little girl when the referee refuses to give him a free-kick for a challenge that was perfectly fair. It's no surprise, really. After all, he did learn from the master.

67 min: Manchester United substitutions: Ryan Giggs and Dimitar Berbatov on, Tevez and Anderson off.

68 min: Cristiano Ronaldo capitalises on sloppy play by Fabregas, latches on to a loose pass, gallops forwards and unleashes a dipping shot that fizzes over Almunia's head and rattles the cross-bar. That was millimetres away from being a marvellous goal. Arsenal could easily be four or five down at this stage,

70 min: Arsenal substitution: Theo Walcott off, Nicklas Bendtner on.

71 min: "Right clicking and 'open in new window' involves two button clicks and is somewhat time-consuming," writes Adam Kingston. "I find Ctrl+click more convenient, except when my other hand is busy (with Monster Munch, obviously)."

72 min: Great work by Rooney, who does well to set up a chance for Michael Carrick, who drives a low shot from distance a couple of feet wide of the left upright.

73 min: From the right flank, Rooney crosses from the right wing. Ronaldo and Toure rise together on the edge of the six-yard box, but the Arsenal player wins the challenge and gets the ball out of harm's way.

74 min: Arsenal are getting torn apart here. Great skill from Berbatov, who engages in a spot of ball-juggling while standing on the edge of the Arsenal penalty area with his back to goal. He dinks the ball to Ronaldo, who picks out Rooney on the left. He attempts to cross for Berbatov on the far post. Almunia intercedes.

77 min: Sixteen. That's how many fouls the ref's blown for tonight. He's been excellent and hasn't put up with any guff from players going to ground and appealing for free-kicks they don't deserve.

78 min: Ryan Giggs gets the ball into the Arsenal net, after splitting the porous defence and latching on to a wonderful through-ball from, I presume, Carrick wide on the right. He's flagged for offside, but replays show it was very tight. On the touchline, Fergie whacks his hairdryer on 11 and turns it on the fourth official.

81 min: This has been the story of Arsenal's night. Lots of tippy-tappy passing in the final third, without them ever looking likely to penetrate Manchester United's defence. Diaby eventually gets a cross into the box, but Vidic hacks clear.

83 min: Arsenal substitution: Adebayor off, Eduardo on.

84 min: Free-kick for Arsenal, wide of centre about 40 yards out from the Manchester United goal. Fabregas sends it into the mixer, where Ferdinand, Bendtner and Van Der Sar contest it in the air on the edge of the six yard box. Bendtner wins the header but gets too much skull on the ball and puts it over the bar. A gentler glancing header might have resulted in a goal.

87 min: Rio Ferdinand's had to go off after that challenge, nursing what looks like an injured rib. It doesn't look too bad, though. He's replaced by Jonny Evans.

88 min: "Just middle click on links, people ... should work on any modern browser," writes Jon in Berlin. I have a better idea, nerdy IT crowd. Why don't you all get a room with a big bed, get nekked, have some long overdue sex for the first time and then discuss link-click optimisation as part of your pillow-talk?

90+1 min: Assuming United don't score in the remaining couple of minutes of added time, Arsenal can consider themselves well and truly blessed to have got out of Old Trafford tonight with nothing more than a one-goal deficit to overcome in the second leg. But for Almunia's heroics and some dodgy finishing, this tie would be over.

90+2 min: Here's a sentence you probably won't have read before: stout defending from Dimitar Berbatov, who puts the ball out for a throw-in deep inside his own half.

Peep! Peep! Peep! Danish referee Claus Bo Larsen, who's been excellent tonight, brings the first leg to a close. Arsenal improved on their first-half performance after the break, but couldn't have been much worse, truth be told. United have squandered chance after chance after chance tonight and could have ended this tie as a contest in the first 45 minutes. Only time will tell whether their profligacy in front of goal will come back to haunt them.

And finally: "Matt Cobb is a friend of mine I haven't seen since 1973," writes Russell Richardson. "We only communicate now via Guardian MBMs. Hi Matt. Is this the most abstruse use of an online feature yet?" I'll get back to you with an answer to that question when I've looked up the meaning of the word abstruse, Russell.