Five games into the new season Serie A is already beginning to feel as though it has been split into two separate divisions. At the top is a two-team league contested by Roma and Juventus, each of whom maintained their perfect starts on Saturday. Below them is an 18-team second tier, the winner of which will be rewarded with a place in the Champions League’s play-off round.

Internazionale have been among the favourites to conquer this division within a division. They began this weekend with eight points from four games, as well as the best goal difference in Serie A. But then they lost 4-1 to last-placed Cagliari. Gazzetta dello Sport accused the Nerazzurri of “Oscar-worthy arrogance”.

But if theirs was a performance worthy of a Razzie, then it helped to build the anticipation for Sunday night’s main feature. The Derby della Lanterna already had something of a Hollywood feel, with Sampdoria wearing a Sin City logo on their shirts thanks to a marketing deal struck by their film-producing owner. And now it had an extra layer of plot intrigue, as the Blucerchiati sought to move above Inter and up to third in the table.

Unbeaten going into the weekend, Samp had already been one of this season’s pleasant surprises. Despite shortcomings up front, they have out-muscled and out-hustled their opposition on the way to wins over Torino and Chievo, as well as draws away to Sassuolo and Palermo. Sinisa Mihajlovic transformed their outlook when he took charge last November – they were 18th when he arrived – and they are now playing more and more in his image.

Their neighbours, Genoa, however, have also started this season in encouraging form. Their one defeat was scarcely deserved, a 2-1 loss to Napoli that arrived courtesy of a 95th-minute Jonathan De Guzman goal. Genoa have beaten Lazio since then, and taken impressive points from tough away games against Fiorentina and Verona.

It all added up to an electric atmosphere at the Marassi on Saturday. In a stadium that is routinely described by Italian newspapers as the “most British” in the peninsula, Genoa’s supporters sang a spine-tingling rendition of You’ll Never Walk Alone while displaying an enormous St George’s Cross.

The flag forms part of their club crest, while the chant is an homage to the 1992 side which won at Anfield – the first Italian team ever to do so. It was previously sung on a sporadic basis, but fans in the Gradinata Nord decided at the start of this season to make the song into a regular pre-game tradition.

Sampdoria’s supporters played their part, too, despite officially being the ‘away’ team. “Overwhelm the enemy,” read the banner hanging in the Gradinata Sud. “Make this battle your own.”

That message felt apt for a match that quickly descended into a form of unarmed combat. The tone was set as early as the fourth minute, when Stefano Okaka was bundled into an advertising hoarding by a Genoa defender, smacking his head in the process. Soon, the Sampdoria forward was squaring up to two opponents in midfield.

Both sets of players managed to keep their heads, but equally both trod a fine line with their robustly physical approach. Although no one was sent off, the two teams combined for 45 fouls and seven yellow cards by the end of the game.

It was not a match rich with goalmouth action. Genoa, more direct in their passing, fashioned more shots on goal but Sampdoria’s Emiliano Viviano still only had four saves to make. Possession was split precisely 50-50. As the game approached its final quarter hour, a goalless draw seemed only likely conclusion.

But then Sampdoria won a free-kick on the right. Angelo Palombo made a dummy run at the ball, before Manolo Gabbiadini swept an in-swinging cross towards the back post. It missed all of Sampdoria’s players in the middle but took the lightest of touches off the head of defender Sebastien De Maio before nestling in the corner of the net.

The goal should not have stood. Several Sampdoria players appeared to be in offside positions when the delivery was made, and although none got a touch on the ball, all were clearly active and interfering with play. “They jumped, they influenced [goalkeeper Mattia] Perin, they are not passive,” protested the Genoa manager Gian Piero Gasperini at full-time. “This uncertainty is a problem, there is total confusion on this rule.”

It was Sampdoria’s sixth goal this season, and five of those have come from set-pieces – a trend which suggests they might be learning more than just tactics from their manager. One of the all-time great free-kick takers, Mihajlovic has not been shy about offering practical demonstrations. At a certain point last season, Palombo and Enzo Maresca challenged him to a post-training competition – and each departed €50 poorer.

Mihajlovic gloated that evening, taunting his players for having the audacity to believe they could match him. But on Sunday he was in a more magnanimous mode. “Beyond the result,” he said, “I want to applaud all the fans [of both teams] because the spectacle given by the crowd was exceptional. To see those stands, those choreographies, is a joy for those of us down on the pitch.

“And I applaud all the players, too, for giving life to a man’s derby – hard, heart-felt, but not nasty. As I said before the game, this is the derby that the city of Genoa deserves.”

Talking points

• So, what exactly did happen to Inter at San Siro? For all that Zdenek Zeman’s teams have tended to score goals in bunches, Cagliari have not looked much like doing so in any game before Sunday. They were aided not only by Yuto Nagatomo’s 27th-minute sending off but also by some catastrophic defending from his team-mates. Nemanja Vidic, signed to bring leadership to Inter’s defence, has now been sent off in one game, given away a cheap goal in another, and then surrendered a penalty on Sunday. It speaks to how poorly Inter played that the spot-kick in question was saved, and yet they still lost 4-1. Nevertheless, hats off to Cagliari midfielder Albin Ekdal for an improbable hat-trick. In a single afternoon, the 25-year-old doubled his career scoring tally.

• After drawing away to Empoli on Tuesday, Milan did the same against another newly-promoted club, Cesena, at the weekend. Fernando Torres was subdued in his second game for the Rossoneri, and Pippo Inzaghi acknowledged the difficulty of trying to make his team work with four forwards – the Spaniard, plus Jérémy Ménez, Keisuke Honda and Giacomo Bonaventura – all in it at the same time. “But I prefer to seek balance while trying to entertain the fans,” he said. And were it not for a blunder by goalkeeper Christian Abbiati, his team might still have won this game.

• Francesco Totti celebrated his 38th birthday on Saturday (and you can read a piece from me about his career right here), but it was his team-mate Mattia Destro who served up a goal of the season contender during Roma’s win over Verona, volleying home from 40 yards.

• Yet another clean sheet for Juventus this weekend – they have now gone 10 games without conceding in all competitions – but positive signs at the other end of the pitch, too. Álvaro Morata opened his account for the club during a 3-0 win over Atalanta, while Carlos Tevez grabbed the other two – giving him six goals now in five games this season.

• Some relief, at last, for Rafael Benítez, as Napoli won 1-0 away to Sassuolo. It was, once again, not a wholly convincing performance from the Partenopei, but at this stage they will be grateful just to have another three points under their belts.

• Brit-watch: Micah Richards made his first start for Fiorentina on Saturday, replacing Nenad Tomovic in the starting XI at right-back. He put in a solid game, getting up and down the pitch nicely even if he admitted afterwards that the adjustment continues to be a struggle. “Italian football is much more tactical than English football,” he said. “I am doing my best to learn as quickly as I can.” It may be tough for him to hold down the spot at right-back, as Tomovic has made a very bright start to this season, but certainly Richards did his cause no harm on Sunday, and his versatility is already being regarded as an asset in Florence.

Results: Atalanta 0-3 Juventus, Cesena 1-1 Milan, Chievo 1-1 Empoli, Genoa 0-1 Sampdoria, Inter 1-4 Cagliari, Roma 2-0 Verona, Sassuolo 0-1 Napoli, Torino 1-1 Fiorentina