Robin van Persie returned to punish his former club by scoring an equaliser as newly crowned Premier League champions Manchester United compromised Arsenal's Champions League hopes in a feisty 1-1 draw on Sunday.
Back at Arsenal for the first time since his £24 million ($37 million, 28 million euros) transfer to Old Trafford in 2012, Van Persie netted a cool penalty just before half-time to cancel out Theo Walcott's early opener.
It could prove a costly goal for Arsenal, who failed to reclaim third place from Chelsea and now find their hold on the fourth and final Champions League qualifying place under threat from Tottenham Hotspur.
Arsene Wenger's side trail Chelsea by one point and lead Spurs by two, but they have played a game more than both their London rivals.
"We will only know at the end of the season (if it was a good result)," Wenger told Sky Sports.
"But it keeps our unbeaten run going. We put a lot of energy into this game, and that's very positive."
The draw left United 14 points clear of Manchester City, although they can no longer fulfil manager Alex Ferguson's wish of breaking Chelsea's Premier League points record of 95 from the 2004-05 campaign.
"We always looked a bigger threat, but that's not taking away the fact that Arsenal put a lot into the game today," said Ferguson. "They worked their socks off, and credit to them."
Fresh from scoring the hat-trick against Aston Villa on Monday that gave United the title, Van Persie received a hostile reception in his first game back at the Emirates Stadium since his acrimonious departure last year.
The Dutchman even walked towards the home changing room on his arrival at the ground, before realising his error.
There was no confusing the Arsenal fans' feelings towards their former idol, however, with boos raining down on him as the home side welcomed the champions onto the pitch with a guard of honour.
Wenger described the reaction as "disappointed love", and to the delight of the home support, the United number 20 was to lose his bearings again to costly effect in the second minute.
His crossfield pass inadvertently found Arsenal full-back Kieran Gibbs, who in turn picked out Tomas Rosicky, and from the Czech's through ball, Walcott beat David de Gea to put the hosts ahead, despite a suggestion of offside.
Pressing United high up the pitch and snapping into tackles, Arsenal's play brimmed with purpose, while the carelessness in the visitors' play suggested the title had been celebrated with a little too much abandon.
Santi Cazorla worked De Gea with an effort from range and the United goalkeeper also had to box away a shot from Lukas Podolski after Cazorla robbed Antonio Valencia of possession.
Gradually, though, Van Persie's influence grew. He teed up Phil Jones for a headed chance that should have yielded a goal, before drawing a superb star-jump save from Wojciech Szczesny with a close-range header.
He was also booked, for sliding in on Per Mertesacker, but he finished the half by sweeping a 44th-minute equaliser past Szczesny from the penalty spot after he had been felled by Bacary Sagna inside the Arsenal area.
It was his 25th league goal of the season but his celebration was respectfully muted.
The sides took to sparring in a less keenly contested second half, with Rosicky poking a shot wide for Arsenal, while Rafael da Silva fired over at the other end and Wayne Rooney headed straight at Szczesny.
Cazorla then whipped a free-kick wide after Valencia had been penalised for a handball right on the corner of the United box, with referee Phil Dowd ignoring the hosts' claims for a penalty.
Laurent Koscielny volleyed over from a corner and Cazorla extended De Gea with a long-range drive, while substitute Ryan Giggs came close to snatching victory for United at the death with a shot that was deflected just wide.