Swansea came from behind with two late goals to claim a memorable win over Arsenal at the Liberty Stadium.
Arsenal took the lead when Alexis Sanchez finished from close range after an excellent run and pass from Danny Welbeck.
But a stunning Gylfi Sigurdsson free-kick and a fine header from substitute Bafetimbi Gomis sealed Swansea’s victory.
The win sees Garry Monk’s men leapfrog the Gunners into fifth place in the Premier League table.
For Arsene Wenger’s side, meanwhile, defeat caps a miserable week after their Champions League collapse against Anderlecht on Tuesday, in which they threw away a three-goal lead to draw 3-3.
There were some nervy moments from the Gunners’ defenders, with Calum Chambers surviving a Swansea penalty appeal after appearing to shove Wilfried Bony to the ground inside the area.
Arsenal did not manage a shot on target until a minute before half time, as Welbeck combined well with Sanchez before his effort was palmed away by former Gunner Lukasz Fabianski.
Arsenal’s flashes of danger before the break were a sign of things to come, as they made the stronger start to the second half.
Alex Oxlade-Chamberlain wasted an excellent opportunity when his shot was saved by Fabianski, but the Gunners were ruthless with their next effort.
The visitors latched on to a poor pass from Bony and launched a counter-attack, from which Welbeck sped into the box, turned past Ashley Williams and squared the ball for Sanchez, who fired in from six yards.
Clear scoring opportunities were at a premium in the first half as two slick but congested midfields cancelled each other out.