Arsenal was punished for a wasteful second half as Swansea City completed a Premier League double over the Gunners with a 1-0 win on Monday.
Lukasz Fabianski came back to haunt Arsenal as Bafetimbi Gomis returned from injury to grab a dramatic late winner for Swansea City in Monday's 1-0 victory at the Emirates Stadium.
After a forgettable first half, Arsenal pummeled the Swansea goal after the break, but Polish goalkeeper Fabianski - who joined Swansea in the offseason after a seven-year spell in north London - made a string of superb stops to deny the likes of Alexis Sanchez, Nacho Monreal and Theo Walcott.
And Fabianski's contribution proved priceless as Gomis - who came on as a second-half substitute following a month-long layoff with an ankle injury - headed home an 85th-minute winner, with goal-line technology showing the ball clearly went in despite David Ospina's best efforts.
It was the second time Gomis has scored against Arsenal this term after he netted in Swansea's 2-1 home win in November, and Garry Monk's side maintained its challenge for a sixth-placed finish that will offer Europa League football should Arsene Wenger's team beat Aston Villa in the FA Cup final.
Arsenal, meanwhile, has surrendered the advantage in the race for second to Manchester City with just two games remaining. The Gunners are three points behind City with one game in hand, but are nine behind in goal differential.
Wenger named the same starting XI for the fifth straight match, and the home side had the first sight of goal when Olivier Giroud nodded Aaron Ramsey's cross over the bar.
Arsenal had tentative penalty claims waved by away referee Kevin Friend in the 27th minute when Alexis Sanchez claimed he was tugged to ground by Neil Taylor from a Santi Cazorla free kick.
Arsenal continued to dominate possession as the half wore on, but aside from a 25-yard effort that Giroud curled wide, the Gunners failed to trouble Fabianski.
There was more intent about Arsenal's game after the restart and Federico Fernandez made a superb sliding block from Hector Bellerin's low center from the right to deny Giroud a chance at goal.
Soon after, Giroud's clever flick was pounced upon by Sanchez who showed great strength to hold off Fernandez before shooting into the side netting.
Arsenal continued to surge forward and Ramsey rifled into the side netting, before Cazorla dug out a shot from the edge of the penalty area that Fabianski saved well low to his right.
Fabianski was in unbeatable form, with Wenger left scratching his head when the Pole denied Monreal one-on-one before making a fine double save from Sanchez and Walcott in the 78th minute.
And Arsenal's profligacy was punished five minutes from time, as Taylor chipped in a cross from the left and Gomis leapt highest to head home, with Ospina's attempted save not enough to prevent the ball from crossing the line.