By Chris Harris at the Liberty Stadium
Two goals in three minutes condemned Arsenal to defeat at the Liberty Stadium on Sunday.
Alexis Sanchez gave the Gunners a second-half lead, slamming home Danny Welbeck's pass from close range after a quickfire counter-attack.
But Swansea hit back and turned the game on its head with 15 minutes remaining.
Gylfi Sigurdsson curled a perfect free-kick into the top corner from 30 yards and substitute Bafetimbi Gomis headed past Wojciech Szczesny with his first touch.
It was harsh on Arsenal, who had opted for a safety-first approach in the first half before showing more attacking intent after the interval.
The visitors were compact and disciplined for most of the game, but they faltered after securing the advantage they had worked so hard for.
SETTING THE SCENE
Wenger made one change for this trip to south Wales - and that was enforced. Mikel Arteta's mild hamstring strain left a vacancy in midfield and Mathieu Flamini filled it. Jack Wilshere returned to the squad after illness but he started alongside Theo Walcott on the bench.
Arsenal went into the game on a decent run - unbeaten in five - but chastened after surrendering a three-goal lead against Anderlecht in midweek.
Swansea were enjoying their best start to a Premier League season and fielded two former Gunners. Lukasz Fabianski - one of Arsenal's FA Cup heroes last season - was their last line of defence, and 2009 Youth Cup winner Kyle Bartley started his first Premier League game of the season.
Before the match, the Liberty Stadium fell silent to mark Remembrance Sunday.
Caution was the watchword in the early stages as Arsenal got back to basics. They were compact, organised and disciplined, probing patiently and keeping men behind the ball. It was necessary after Tuesday night, but it made chances hard to come by.
Swansea, shorn of Nathan Dyer and Wayne Routledge, took time to get going too. But they grew in confidence and found joy down Arsenal's right flank through the lively Jefferson Montero.
The Ecuadorian forced a sharp stop from Szczesny at his near post, seconds after Wilfried Bony had a penalty claim turned down following a barge in the back from Chambers.
Szczesny was called into action again 10 minutes before half-time when Bony set up Marvin Emnes, but Arsenal finished the half strongly.
They came alive with a slick passing move that culminated in a sharp one-two between Ramsey and Welbeck, but Fabianski kept out Welbeck's effort at his near post.
Ramsey himself went close moments later with a brilliantly volley which had Fabianski beaten but flew inches wide. Then Per Mertesacker, making his 100th Premier League appearance, sent a towering header off target.
Arsenal's attacking intent - glimpsed at the end of the first half - was much more obvious after the break.
The visitors almost went in front within seconds, Alexis seizing possession on the halfway line and slipping in Oxlade-Chamberlain, but the England man had the ball under his feet as he shot and couldn't get the power to beat Fabianski.
Nonetheless, Oxlade-Chamberlain was an increasing influence. Relishing his battle with Neil Taylor with the left back on a yellow card, Oxlade-Chamberlain took on his man time and again.
One surge ended with a good ball to Welbeck, but the striker couldn't return the favour. However, the international team-mates were involved in the move that gave Arsenal the lead in the 63rd minute.
The Gunners broke at pace and Oxlade-Chamberlain ran at the Swansea defence before Cazorla played in Welbeck. He had options inside the box and had the presence of mind to cut back inside and pick out Alexis, who found the net.
Bony had a clear sight of goal after Montero got to the byline, but the Swansea striker got his shot all wrong. The warning signs were there though and the home side turned the game on its head in the space of three minutes.
The first goal was world-class - Sigurdsson firing a stunning free-kick into the top corner with Szczesny at full stretch. And the Arsenal keeper was helpless again two minutes later as substitute Gomis headed in Montero's cross.
Arsenal had hoped to pick Swansea off on the break; instead they had to break them down again. On came Walcott and Wilshere in an attempt to rescue the situation.
Walcott had a half-chance but couldn't control a ball over the top when he just had Fabianski to beat.
The final opportunity fell to Wilshere in stoppage time but his attempt to connect with Oxlade-Chamberlain's cross was thwarted by Bartley - his old Youth Cup team-mate.
Referee: Phil Dowd
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