Arsenal completed a terrible week for hanging onto leads as let it slip at Swansea.
Alexis Sanchez had given the Gunners the lead in the second half but a freekick from Gylfi Sigurdsson 15 minutes from time and a header from Bafetimbi Gomis completed the turnaround in rain-soaked South Wales.
It came a few days after they squandered a three goal lead at home to Anderlecht in the Champions League to draw 3-3.
Theo Walcott made the bench again as he continued his return from a long injury layoff and was joined by Jack Wilshere – also returning after two and a half weeks out.
Swansea had the better of the opening exchanges; Sigurdsson swung over a freekick which Calum Chambers headed away while Angel Rangel had a shot after a good run and cross from Neil Taylor.
The Swans wanted a penalty after 20 minutes when Wilfried Bony was shoved in the back by Chambers but referee Phil Dowd waved all appeals.
Arsenal wanted a penalty of their own as Oxlade-Chamberlain claimed he was tugged back by Jefferson Montero, but the referee said no.
The first real chance of the game fell to Marvin Emnes after he was fed by Bony but his shot was too close to Szczesny batted it away.
Ki Sung-Yueng and Taylor picked up yellow cards just before the break for the home side, both for rash challenges on Oxlade-Chamberlain before firing at goal, but Fabianski easily palmed it clear.
Ramsey flashed a well-taken volley just wide before Per Mertesacker headed wide from a corner as the Gunners finished the first half the stronger of the two sides.
Arsenal picked up momentum in the second half as Sanchez played in Oxlade-Chamberlain, but his weak left-footed shot was right at Fabianski.
The Gunners continued to pile on the pressure but couldn’t breakdown Swansea’s defence.
In the 60th minute, Carzola fired off a snap shot from just outside the box but it was straight at fabianski. The rain got stronger and as the ground became more slippery the yellow cards followed; Mertesacker, Ramsey and Flamini all went into the book before Arsenal finally found the net.
Welbeck was released down the right and cut inside brilliantly past Williams before squaring to Sanchez who has the simple task of tapping into the net.
Swansea drew level with 15 minutes to go when Sigurdsson curled a superb freekick into the top corner, giving Szczesny no chance.
They completed their turnaround a few minutes later when Bafetimbi Gomis headed in Montero’s cross were minutes after coming on a s a substitute.
Swansea now sit in fifth position as Arsenal drops to sixth.