Manchester United saw their defense breached for the first time in the Premier League this season as Swansea City came from behind to secure a 2-1 victory at the Liberty Stadium. In Louis van Gaal’s 50th match in charge, he tasted a third straight 2-1 defeat to the Welsh side, and just as in the corresponding fixture last season, it was Bafetimbi Gomis who netted the winner. A handful throughout, Gomis stretched his record of scoring in every match this season to four, but both his goal and Swansea’s win owed a large debt to summer signing Andre Ayew.

The Ghanaian had headed in a cross from Gylfi Sigurdsson just past the hour mark to cancel out Juan Mata’s close-range opener early in the second half. But his best moment was still to come. Five minutes after pulling his team level he played a sublime pass with the outside of his left foot that left Chris Smalling and the rest of the Manchester United defense flat-footed and allowed Gomis to get in behind and sneak a shot past Sergio Romero.

Swansea were without their chief danger man so far this season, Jefferson Montero, to a late injury, but they still had enough to worry a United defense that had been the best feature about Van Gaal’s side in the early weeks of the season. The visitors had the bulk of possession, attempting to attain the control that Van Gaal so craves. Yet, for the most part, their threat in the final third was once again limited. Wayne Rooney, despite his hat-trick at Club Brugge in midweek was again a blunt force. With just 48 hours of the transfer window remaining, the pressure on Van Gaal to add a striker of proven top quality to his ranks will not abate.

And he may well have renewed doubts, too, about whether he has enough defensively to challenge for the top both at home and in Europe this season. Daley Blind has looked accomplished in an unfamilair role thus far, but was given his toughest time yet by Gomis, who repeatedly looked to exploit the versatile Dutchman. A shaky performance for Sergio Romero, meanwhile, should only increase the urgency to get the David de Gea saga resolved and preferably in time for United to secure a replacement if he is to depart for Real Madrid.

Yet for all Manchester United will be disappointed after dropping further points following their goalless draw at home to Newcastle United, it would be a surprise were many teams to come away happy from the Liberty Stadium this season. Swansea remain unbeaten and remain a model for all clubs of their size for how to consistently improve despite losing key components to the Premier League’s richer operators. And the capture of Ayew, a player who could surely make an impact at top-four level, continues to look one of the coups of the summer.

Manager Garry Monk contributed much to a memorable win, too, though it was a difficult opening for his men. Manchester United begun the game with an impressive intensity with and without the ball and had the hosts under pressure. In what has been a recurring theme, though, they could not capitalize, in no small part due to the sluggishness of Rooney up front. Three times the England forward managed to get in behind the Swansea defense, but on each occasion he lacked decisiveness, with Ashley Williams twice getting back to thwart him.

Much of the first half saw the two teams, playing similar systems and with an emphasis on pressing their opponents, cancel each other out in a tight midfield battle. But Swansea had enjoyed the best of the first-half chances in a blistering five minute spell midway through the opening period. Gomis twice couldn’t find the target, with the former Lyon forward first slicing wide and then seeing an effort clip the outside of the post. An even better opportunity fell to Sigurdsson, but he, too, was wayward with the finish.

It appeared that profligacy might be costly when United earned a reward for their quick start to the second half. Luke Shaw got the benefit of a ricochet to break clear down the left, before his cross was left by Rooney and Mata arrived at the back post to finish into the roof of the net from a tight angle.

Especially after Williams almost turned the ball into his own net soon after, United might have been expected to go and secure a welcome three points. But Monk’s tactical shift in response to his side going behind paid handsome dividends. With Ki Sung-yueng replacing Wayne Routledge, Swansea moved Ayew into a more influential forward role to support Gomis.

Almost immediately he arrived on cue in the box to complete a quick Swansea breakaway by heading in Sigurdsson’s cross from the right for his third goal in a Swansea shirt. His pass soon after was a moment of magic, although United will still have reason for disappointment they first failed to cut it out and then that Romero allowed Gomis’ fairly tame effort past him at his near post.

Having gone behind, United had no answer. And the fact that Van Gaal’s best option was again to bring Marouane Fellaini on and opt for the aerial route only served to highlight United’s lack of more nuanced attacking options.