West Bromwich - Arsenal missed the chance to go top of the Premier League as they suffered a 2-1 loss away to West Bromwich Albion on Saturday
France international Olivier Giroud headed his ninth goal in 11 matches from a Mesut Ozil free-kick to give Arsene Wenger's visitors hope of a sixth win in seven league matches.
But two lax pieces of defending before half-time, and a late Santi Cazorla penalty miss, allowed West Brom to claim victory - their first over Arsenal at the Hawthorns since 2005.
James Morrison got free to turn in Chris Brunt's free-kick with his shin, before Mikel Arteta diverted a cross into his own net via his arm and his thigh.
It was not the result Arsenal wanted ahead of Tuesday's must-win Champions League tie against Dinamo Zagreb.
Giroud, along with France team-mate Laurent Koscielny, was named in Arsenal's starting line-up after the trauma of being caught up in the Paris attacks eight days ago, in which 130 people died.
Wenger had noted in the build-up to the match that Koscielny, in particular, had been deeply affected by the attacks, which included a number of explosions outside the Stade de France, where France were playing Germany in a friendly.
Arsenal's French manager, though, was satisfied that the central defender was in the right frame of mind to play.
The injury-hit visitors suffered an early setback as midfielder Francis Coquelin limped off after jarring his knee in a challenge with Claudio Yacob.
They did, though, have the better of the opening half-hour, with Alexis Sanchez's floated free-kick well held by keeper Boaz Myhill, and were first to score.
Albion's defence switched off as Ozil's free-kick, swung in from the right, was glanced in by an unmarked Giroud.
Arsenal's advantage lasted just five minutes, however, as they were undone by a set-piece at the other end.
Brunt lifted in a free-kick from just inside the visitors' half, and Morrison sneaked in behind Hector Bellerin to volley the equaliser from seven yards.
It got worse for Arsenal five minutes before half-time, with the excellent James McClean doing the damage.
McClean, who had caused problems with an early low ball that whizzed across goal, burst past Bellerin on to Salomon Rondon's pass, and drove in a delivery that was turned into his own net by Arteta, on as a substitute for the injured Coquelin.
Arteta, who had a thoroughly forgettable afternoon, was himself replaced by Mathieu Flamini just three minutes into a second half that the visitors dominated.
By then, Arsenal had almost drawn level, with Giroud seeing a penalty appeal rejected as he tangled with Jonas Olsson at a free-kick, then hitting the inside of the post with a terrific low shot on the turn.
Only a superbly-timed by West Brom's Jonny Evans challenge prevented Ozil from connecting with a Sanchez through pass.
But still the visitors could not find an equaliser, with substitute Joel Campbell skewing back across goal when Cazorla's diagonal chip found him free six yards out.
At the other end, Albion centre-back Jonas Olsson went close with a header that bounced down off the bar, but referee Mark Clattenburg ruled that Saido Berahino had been standing in an offside position.
Despite going close there, the home side were largely holding on through the closing stages, and looked set to be caught when Brunt was judged to have pushed over Sanchez with seven minutes left.
But Cazorla slipped as he took the resulting penalty, sending the ball looping over the crossbar.