Arsenal was beaten 2-1 by West Bromwich Albion in the Premier League on Saturday and lost two more players to injuries on a day when everything went wrong for the Gunners.
Arsenal captain Mikel Arteta deflected a cross into his own in the 40th minute to hand West Brom the winning goal and Santi Cazorla missed a penalty in the 84th when he slipped as he was about to shoot.
Olivier Giroud had given Arsenal the lead by heading in a pinpoint free kick from Mesut Ozil in the 28th but James Morrison equalized by steering in a similar delivery at the other end in the 35th.
Aside from losing ground in the title race, Arsenal's injury concerns also grew worse. Arteta had to come on for Francis Coquelin in the first half after the holding midfielder hurt his knee, only to go off injured himself shortly after the break. Arsenal was already without a slew of players, including Theo Walcott, Aaron Ramsey and Alex Oxlade-Chamberlain, and immediately looked defensively weaker without Coquelin.
Morrison was poorly marked on the equalizer when he looped a 10-yard volley over Petr Cech after Chris Brunt's excellent free kick.
Five minutes later, Salomon Rondon and James McClean combined and Arteta turned in McClean's cross from close range. The Spanish midfielder's disappointing afternoon ended three minutes after the break when he limped off to be replaced by Mathieu Flamini.
Arsenal dominated much of the second half but struggled to create clear-cut chances. Substitute Joel Campbell wasted the best opportunity in the 68th when he met Cazorla's cross but mishit the ball as he tried to sidefoot it into the net.
Cazorla then had the chance to level after Alexis Sanchez was pulled down in the area but skied the ball over the bar after losing his footing.
The loss meant Arsenal slipped from second to fourth place, while West Brom climbed to 12th.