Arsenal have lost three games in a row for the first time in almost six years and missed the chance to close within three points of Premier League leaders Leicester City by losing 2-1 at home to struggling Swansea City.
Swansea, whose manager Francesco Guidolin missed the match because of a chest infection, made several changes from Sunday's defeat at Tottenham Hotspur, resting the likes of Gylfi Sigurdsson and Alberto Paloschi ahead of Saturday's visit of Norwich, and Arsenal dominated the early stages.
Alexis Sanchez rattled the post in the 11th minute and soon after the hosts were in front as Joel Campbell swept home on the stretch from Sanchez's floated pass.
Mesut Ozil and Hector Bellerin threatened a second for the Gunners, while down the other end Swansea's first menacing moment came when Leroy Fer curled just over the top.
The Swans then levelled in the 32nd minute through Wayne Routledge, who ended a 34-game goal drought in the league by slotting home Jack Cork's pass after Ozil lost the ball in the centre circle.
Arsenal went close to restoring their advantage before half time when they struck the woodwork for a second time, with Olivier Giroud this time crashing a volley against the crossbar from Per Mertesacker's cushioned header.
Sanchez was Arsenal's main threat in the early stages after half time and twice went close, first shooting just wide before failing to apply any kind of touch to prod home an Ozil free kick.
In the 65th minute Swansea were inches from taking a surprise lead when half-time substitute Sigurdsson surged into the area and rounded Petr Cech before firing powerfully across goal and behind for a goal kick from a tight angle.
Arsenal then hit the woodwork for a third time through Sanchez's free kick that slapped back off the bar before Swansea took a stunning lead in the 74th minute. Sigurdsson was the creator, whipping a free kick into the six-yard box where Cech could only parry the ball against Swans captain Ashley Williams and into the net.
The visitors then sat back on their lead and Arsenal could not create many clear openings in the closing moments of the game, with Nacho Monreal, Giroud and Danny Welbeck all guilty of failing to really test Lukasz Fabianski in the Swansea goal.
It is a first win in five for Swansea, who are now unbeaten in four games at the Emirates, and they edge six points clear of the relegation zone. Arsenal stay third but remain six adrift of Leicester and three behind rivals Tottenham Hotspur, with the North London derby next on Saturday lunchtime.
