Santi Cazorla slipped and missed a late penalty as Mikel Arteta’s own goal condemned Arsenal to a 2-1 defeat at West Brom.
The Gunners, who had won five of their last six away games, took the lead when Olivier Giroud nodded in Mesut Ozil’s pinpoint free-kick.
But the Baggies hit seven minutes later after Chris Brunt’s free-kick was steered into the net by James Morrison.
And they grabbed the lead when substitute Arteta, who was on for the injured Francis Coquelin, turned in James McClean’s cross with his hand for a bizarre own goal.
The Gunners had a nightmare second half with Arteta going off with a calf injury, Joel Campbell missing a sitter from six yards before Cazorla blazed his penalty over the bar after slipping as he struck the ball.
Tony Pulis’s side move into 11th place with the win while Arsene Wenger’s men slip to third.