Joel Campbell gave Arsenal the lead with a quarter of an hour played, but English winger Wayne Routledge equalised just past the half-hour mark. Swansea captain Ashley Williams fumbled in a winner for the visitors 15 minutes from time as Arséne Wenger's side lost back-to-back games for the first time in the league this season.
The result also means that Arsenal go six points behind Premier League leaders Leicester and three points on Spurs, who they play on Saturday.
A promising start
The Gunners started the game on the right foot, causing multiple problems for the Swansea defence within the first five minutes, however Olivier Giroud could not convert the three good chances that came his way with three identical weak shots. Alexis Sánchez went close to ending a run of poor form by almost finding the net 12 minutes in, when the Chilean winger smacked the inside of the post with a wicked shot from close range, and Lukasz Fabianski caught the spinning ball.
It looked to be the usual story for Arsenal, having too many shots at goal and failing to score, however the tides looked to have changed as Campbell fired Arsenal ahead in the 15th minute. Campbell made a darting run into the penalty box, where Alexis picked out the winger with a lofted ball over the Swansea defence, and the Costa Rican slide the ball past Fabianski with a great finish on the slide, to give Arsenal an early lead.
The home side were playing with a rare confidence as Hector Bellerín almost made it two in the 25th minute when the Spaniard fired from 25-yards out, however the former Arsenal man did well to hold onto the powerful strike from the talented young right-back.
Same old Arsenal
However, Arsenal fell back to planet Earth when Wayne Routledge equalised for the visitors in the 32nd minute.
Mesut Özil lost possession of the ball in midfield - which was later adjudged to be a foul - to which Jack Cork pounced onto, the midfielder then slid the ball past the Arsenal centre-backs to Routledge, who easily finished the ball past Petr Cech, to make it 1-1. Despite the shock equaliser, Arsenal responded well 11 minutes later when Per Mertesacker teed off the ball for Giroud inside the penalty box, but the France international smashed the ball off the crossbar with a mean right-footed volley.
The second-half kicked off with very little excitement or action, unlike the first-half both teams looked adamant on trying any form of attack. Alexis had the first real effort on goal in the 54th minute when the former Barcelona attacker fired inches wide from close range after a promising set-piece from Mesut. Alexis came close again from an Ozil set-piece when the German international picked out the Chilean inside the penalty box with a great whipped in free-kick, but Sánchez failed to make contact with the ball, and Fabianski collected the free ball gratefully as the pressure was relieved.
Wenger then made the bold move to replace Campbell, who had been Arsenal’s best attacking player all game, with Danny Welbeck in the 64th minute, a decision that was met with jeers from the Arsenal crowd. Swansea substitute Gylfi Sigurdsson should had made it 2-1 to the travelling team after the former Tottenham playmaker skipped over Cech, but the angle was too hard for the Icelandic international to convert the ball into the open net.
Alexis was again close to giving Arsenal the second goal they needed when the crossbar was hit yet again by Arsenal when the winger smacked the bar from a close range free-kick.
However, it was the visitors that would claim the second goal as the captain, Ashley Williams, made it 2-1 to Swansea City in the 76th minute. Sigurdsson whipped in a free-kick from just outside the penalty box in a crowded area, and the ball fell to Williams, who knew little about the ball, and the ball fumbled its way past Cech, to give the visitors the lead.
Arsenal tried to salvage a late comeback, but by then the team and the fans looked to have given up in the game, and Swansea went onto the record a massive three points as Arsenal yet again slip up as the race for this year's League crown continues to intensify.