The Gunners\' lead at the third spot is cut to five points with Spurs and Newcastle having a game in hand.
London: Wigan backed up their shock victory over Manchester United by beating another Premier League giants on Monday, winning 2-1 at third-place Arsenal to boost their hopes of staving off relegation.
Arsenal were looking for a victory that would have put them eight points clear in third but never recovered from sloppily conceding goals to Franco di Santo and Jordi Gomez in the first eight minutes.
Thomas Vermaelen halved the deficit in the 21st but the visitors held on quite comfortably in the end to record yet another superb victory in their battle to stay up, moving them five points clear of the relegation zone with four matches left.
"We've had a difficult time and have had to stick together and really stay strong as a group and we've done that," said Wigan captain Gary Caldwell, who kept league top scorer Robin van Persie quiet at Emirates Stadium. "There's still a long way to go and it's still going to be a real battle at the bottom."
Roberto Martinez's side stunned league leaders Man United 1-0 on Wednesday and has also beaten Liverpool away in the past month.
Wigan's only loss since the start of March came at Chelsea, who scored two goals that should have been disallowed for offside, including an injury-time winner.
"We have always had a mental block against the top sides, but we went to Liverpool and got rid of that," Martinez said. "And against Manchester United and Arsenal, nobody can deny that we deserved the points."
Arsenal's first loss at home since Jan. 22 will give renewed hope to their three rivals for the remaining two Champions League qualification spots.
Spurs and Newcastle are five points behind while Chelsea are a further two adrift. All three have a game in hand over Arsenal, who have four more matches left.
"We were not sharp," Arsenal manager Arsene Wenger said. "It's difficult to know why."
While Wigan relied on their slick passing game to defeat United, drawing plaudits from opposing manager Alex Ferguson, Martinez's men were helped out by some poor defending at Emirates Stadium.
An untimely injury to Mikel Arteta left the hosts short at the back as Wigan raced clear on the counterattack following an Arsenal corner. Gomez's cross from the left was met by a shot by Di Santo that was blocked by goalkeeper Wojciech Szczesny, but the ball looped up kindly for the Italian striker to volley in from close range.
Arteta was off the field — to be soon replaced by Aaron Ramsey with what Wenger said was a "serious" ankle injury — when Wigan grabbed their second. Szczesny saved from Di Santo following good work down the left by Victor Moses, only for Gomez to apply the tap-in.
"We defended horrendously on the first and second goals," Wenger said. "After that we had a mountain to climb."
There were only 94 seconds between the two goals and, having lost all six of their Premier League matches at Arsenal, Wigan were in uncharted territory. The visitors were on the back foot for most of the remaining 82 minutes but were resolute in defense and sprightly on the break.
Indeed, after twice denying Yossi Benayoun and then keeping out Van Persie's snapshot, Wigan goalkeeper Ali Al Habsi was hardly troubled except for Vermaelen's bullet header that flew into the net from Tomas Rosicky's cross.
Arsenal had all the possession but Wigan could easily have restored their two-goal cushion in the 59th when Moses, a danger throughout, went clean through after more defensive carelessness by Arsenal. However, the forward bizarrely elected to shoot early instead of closing in on Szczesny and his weak shot was saved.
Arsenal huffed and puffed in the final 30 minutes but were short of creativity when it really mattered, leaving Wigan to claim an unlikely first win at Arsenal.
"In the second half, we lost our team-play and cohesion and we tried too much individually," Wenger said. "There was no petrol left in the tank."