A vital Dax McCarty away goal was enough to see New York Red Bulls past DC United in the first leg of the MLS Eastern Conference semi-final at RFK Stadium, but New York will return home counting the potential cost of injuries and yellow cards as they eye deeper progress in these playoffs.

DC started the livelier – not allowing the Red Bulls time to impose their favored pressing game and winning most second balls in the early stages.

Fabian Espindola, whose 2014 season had ended in a red card against his former team, at the same stage of the competition last year, looked like a man intent on putting the record straight. From the whistle he began attacking New York’s right back Sal Zizzo from the start, and most of DC’s best work in the opening period came down that flank.

New York, by contrast, were slower to settle, and their few forays forward looked undermanned by their usual pressing standards. Yet despite some scares at the other end, the first clear chance of the game went their way. In the 17th minute Dax McCarty flicked a short ball into the box towards the head of Felipe, who was unmarked, but didn’t seem to realize how much space he had as he powered his header well wide, when a flick might have taken it beyond Bill Hamid.

As it happened, headed chances were the main story of the first half. Alvaro Saborio proved a handful for the Red Bulls defense and had a couple of good looks he couldn’t turn into work for Red Bulls’ goalkeeper Luis Robles, while Sacha Kljestan, whose inventiveness and vision gradually played New York into the game, had a more direct look at goal in the 38th minute but could only head over the bar.

Just before that moment came New York’s best chance of the half, when Bradley Wright-Phillips hooked a loose ball in the box into the path of Mike Grella, near the left of the six yard box. Grella did well to make space for the shot, but Bill Hamid did better in the DC goal to first narrow the angle quickly then keep himself big to block the shot. Hamid didn’t have a whole lot to do in the first 45 minutes, but he ended the half getting down well to smother a Felipe cross with Grella lurking.

Hamid would be busier in the second half, which started as a mirror image of the first, with New York now the clear aggressors. Kemar Lawrence began getting some joy on overlaps down the left and smashed a close range, though narrow angle, shot off Hamid’s right post in the 59th minute, to cap a period of dominance that also saw Hamid acrobatically tip a McCarty header away moments earlier. New York clearly felt that anything less than an away goal to take back for the second leg would count as a failure.

In the 61st minute DC remembered their own home status, as Saborio had a half-chance on a knockdown from Espindola, only to drag his shot wide.

If that cause disquiet for New York, they had other reasons to feel slightly uneasy about how things were going in their own half of the field, especially at the heart of defense. Matt Miazga picked up a first half yellow card, while defensive partner Damien Perrinelle was stretchered off early in the second half after a nasty looking landing on an aerial challenge. His replacement, Ronald Zubar, then picked up a yellow for a lunging challenge on Markus Halsti in the 68th minute. These incidents might not decide the games they occur in, but they have a habit of adding up to affect playoff campaigns.

DC of course, were playing without a starting center back of their own, following Bobby Boswell’s one game suspension for kicking Juan Agudelo off the ball in the knockout game against New England. But their defense looked to be holding their own until the 72nd minute when a Sacha Kljestan free kick was whipped into the box and Dax McCarty dived to head home at the back post, having lost Perry Kitchen with his run.

DC tried to counter immediately – as Espindola turned and hit a rasping shot from distance that didn’t miss by much. It temporarily paused the Red Bulls fans from singing “Twist and Shout” high in the old stadium — though didn’t stop the press box from swaying alarmingly as the away crowd jumped around next to us.

Saborio had been working diligently to track back and help out his midfield in the first half, but had begun to wane in influence to become a more fitful irritant in the second. He picked up a yellow card in the 77th minute for a foul on McCarty, but was otherwise looking more peripheral as DC sat deeper, and with Chris Rolfe having been substituted out for Conor Doyle in the 65th minute, it didn’t often look like there was anyone to link up the play for the home side. As a result, Espindola and Saborio were left more and more isolated up front.

Ben Olsen brought off Sean Franklin for Miguel Aguilar to try and remedy the shape of the team in the 84th minute, but the damage was already done by that point. At times in the second half his team more closely resembled the side that went missing in Columbus last Sunday, rather than the resilient group of players that managed the game against New England in midweek.

There was a brief flurry of enthusiasm from the home crowd as six minutes of time was added on for the Perrinelle injury, but New York were generally coping comfortably with the aerial barrage that followed and saw the game out for a vital win on the road — the first by any team in these 2015 playoffs.

DC have rallied once, in the first game of these playoffs, after the trauma of a record-equalling defeat on the last day of the regular season. Now they must do the same in New York. Easier said than done, even if winning after falling behind has been the story of DC’s season so far. To which New York might point out that their season has been about winning the Supporters Shield when many thought they’d miss the playoffs. They’re very much still in them.

D.C. United: Hamid; Franklin (Aguilar 84), Opare, Birbaum, Kemp; Rolfe (Doyle 65), Halsti, Kitchen, DeLeon; Espindola, Saborio

New York Red Bulls: Robles; Zizzo, Miazga, Perrinelle (Zubar 51), Lawrence; McCarty, Felipe, Sam, Kljestan, Grella (Veron 81), Wright-Phillips