An in-form Crystal Palace handed Arsenal a 3-0 defeat Monday to dent the Gunners' hopes of securing a top-four Premier League finish this season.
Arsenal was put to the sword in the first half by the clinical host, with goals from forwards Jean-Philippe Mateta and Jordan Ayew giving Palace a deserved 2-0 interval lead.
The Londoners improved after the break, with Emile Smith Rowe and Martin Odegaard missing big chances to get their team back in the match. Their wastefulness proved costly as Wilfried Zaha put the game to bed with a penalty 16 minutes from time.
Tottenham Hotspur's 5-0 home victory over Newcastle United on Sunday means it is fourth, ahead of its north London rival on goal difference having played a game more.
The scoreline at Selhurst Park did not flatter an impressive Palace, who continues to improve under former Arsenal captain Patrick Vieira, with the victory moving it up to ninth.
Arsenal had been in fine form on the road in the Premier League prior to its trip across London on Monday.
Its 1-0 win at Aston Villa last time out was the fifth away league victory in a row – the first time it had been on such a run since May 2015.
But it struggled from the start to find any rhythm, with Palace very much the better side in the opening period.
It took the home side 16 minutes to break the deadlock, as Joachim Andersen's head sent a free kick across the box for Mateta to steer in his fourth league goal of the season.
Eight minutes later and center back Anderson again turned provider, picking out a perfect pass for Ayew, who controlled well before finding the net for the first time since December.
Arsenal just could not create any openings of note in the first half, with Mateta going close to adding a third for Palace before the interval.
Content with a two-goal lead, the hosts sat back and invited pressure after the break. Smith Rowe should have done better from close range before Odegaard dragged his effort wide.
Zaha then broke on the counter and was awarded a penalty – only Raheem Sterling (23) and Jamie Vardy (21) have been given more penalties in Premier League history than the Ivory Coast forward – which he converted emphatically.
Arsenal substitute Eddie Nketiah did hit the crossbar but it would have been too little, too late.
A second defeat in its last three league games opens the door for Arsenal's top-four rival and Mikel Arteta's side still has it all to do to secure a return to the Champions League for the first time since 2016-17.
Fifth-placed Arsenal is level on 54 points with Spurs and three points ahead of West Ham United and Manchester United, albeit with all their top-four rivals having played more games.
