Yannick Bolasie struck a hammer blow to Arsenal's top-three hopes with a late equaliser as Crystal Palace secured a 1-1 draw at Emirates Stadium.
The winger was allowed to cut in off the left by the Arsenal defenders with nine minutes to play and he took full advantage with a powerful low shot that beat Petr Cech.
Bolasie's strike was Palace's best sight of goal in the entire 90 minutes as Arsenal dominated possession, the hosts having taken the lead through Alexis Sanchez.
Arsenal wasted a glut of chances to extend their advantage before Palace snatched a point, Mesut Ozil and Danny Welbeck particularly at fault.
The result means Arsenal fail to overtake Manchester City in the Premier League table - pulling level with Manuel Pellegrini's men - and sit just four clear of Manchester United in the race for Champions League football.
Meanwhile, Palace are nine above the relegation zone and face a trip to United on Wednesday before next weekend's FA Cup semi-final with Watford.
There was little to split the two sides in a drab opening 20 minutes, with Arsenal enjoying large swaths possession without being able to find the final ball.
In fact, the best opening fell to Palace, but Scott Dann was unable to get his header on target from Pape Souare's left-wing cross.
Wayne Hennessey continued to be untroubled in the Palace goal as the clock ticked towards half an hour, but counterpart Cech - recalled in place of David Ospina - was called into action by Bolasie's curling effort after 28 minutes.
Arsenal raised the tempo as half-time approached and created chances for Sanchez and Ozil that were wasted, the latter firing straight at Hennessey after exchanging passes with the Chilean.
Sanchez made no mistake in stoppage time, though, as he held off Souare to loop a header over Hennessey from Welbeck's chipped pass - his 10th league goal of the season.
Neat link-up play between Alex Iwobi and Welbeck presented the latter with an early sight of goal after the restart, but the England striker opted for the near post with his effort and Hennessey saved easily.
Ozil's quality from set-pieces began to have a big impact on proceedings around the hour mark, but, after firing wide himself, Welbeck and Sanchez both failed to beat Hennessey.
Palace - who introduced former Arsenal and Tottenham striker Emmanuel Adebayor to a chorus of boos after 63 minutes - punished Arsenal profligacy in front of goal late on, though, with their first real effort on target.
Adebayor cut inside from the left wing and found Bolasie, who evaded two defenders before rifling a low shot past Cech. Despite Arsenal's desperate attempts to grab a winner, the visitors were able to hold on.