Swansea dashed Thierry Henry's hopes of a dream return to the Premier League as they struck a blow to Arsenal's top-four ambitions with a 3-2 win at the Liberty Stadium on Sunday.
Robin van Persie had given the Gunners an early lead only for a Scott Sinclair penalty and a Nathan Dyer strike to swing the contest in Swansea's favour.
Theo Walcott levelled for Arsene Wenger's side in the 69th minute, soon after Henry's introduction as a substitute for his 255th English top-flight appearance, yet the visitors were left stunned a minute later when Danny Graham fired in the winner.
Arsenal could have few complaints with the outcome, though, after a sub-standard display which means they remain four points adrift of fourth-placed Chelsea in fifth position.
They have now suffered back-to-back league defeats and this was a painful reintroduction to the top-flight for French striker Henry, five years after he left Arsenal to join Barcelona.
Mikel Arteta was a notable absentee for the Gunners after picking up an injury in training on Saturday, while their injury crisis at left-back meant Ignasi Miquel earned his first Premier League start.
Swansea made four changes from the team which defeated Barnsley in the FA Cup last weekend yet they found themselves trailing within five minutes following the Gunners' first serious attack.
Welsh midfielder Aaron Ramsey, back in his native country, and Alex Song combined to feed Andrey Arshavin, whose threaded pass set van Persie away and he did the rest, fooling Steven Caulker with a dummy before squeezing a vicious low shot inside the near post.
After scoring 35 goals in 2011, it was the Holland international's first of the new year having recently been given time off by Wenger.
However, the Swans were handed a controversial opportunity to level matters from the penalty spot just 12 minutes later when Dyer turned sharply inside the area before tumbling under the slightest contact from Ramsey.
Gunners goalkeeper Wojciech Szczesny guessed the right way but Sinclair's strike was precisely placed into the bottom corner.
Arsenal squandered a good chance when van Persie went through on goal, yet this time he was foiled by Michel Vorm, who stood up superbly to narrow the angle.
The Gunners fans chanted Henry's name when he emerged from the dug-out to warm-up as they signalled their desire to see their hero make his much-anticipated Premier League return.
They certainly needed inspiration from somewhere as Swansea twice threatened with long-range strikes from the impressive Dyer and Joe Allen.
And it was those two who combined to put Brendan Rodgers' team in front in the 57th minute.
Allen dispossessed Ramsey and squared the ball to Dyer who steadied himself before unleashing a sweetly-struck shot beyond Szczesny.
It was not long before Henry and Tomas Rosicky were introduced for the disappointing Arshavin and Yossi Benayoun and by the 69th minute Arsenal were level.
Johan Djourou carved open the Swans defence to send Walcott clean through and he clipped the ball beyond Vorm.
The visitors' joy was to prove short-lived, though, as within a minute the Swans had regained the lead.
Graham took advantage of some slack defending to clinically convert from a tight angle after good work from substitute Gylfi Sigurdsson.
Henry, back with Arsenal on loan from the New York Red Bulls, made an immediate impact with the winner on his return in Monday's FA Cup victory over Leeds.
Yet he was unable to register his 175th Premier League goal and inspire a turnaround this time as the Swans survived a flurry of late pressure to record a memorable triumph.