Arsenal missed the chance to move back into the Premier League's top four and strengthen their hopes of Champions League football as they were stunned by Crystal Palace at Selhurst Park.
The Gunners would have moved above Tottenham with victory but fell behind early on through Jean-Philippe Mateta's header following a free-kick.
Things got worse for the visitors a few minutes later when Jordan Ayew got away from two Arsenal defenders and bent a shot beyond Aaron Ramsdale.
Arsenal were outfought and outworked in the first half, their only shot on target a Gabriel header at Palace goalkeeper Vicente Guaita.