Gunners held by Baggies
Jack Wilshere rescued a point for Arsenal at West Brom to send them level with Liverpool at the Barclays Premier League summit, but a thrilling 1-1 draw might easily have gone either way.
The Baggies, fresh from downing Manchester United last weekend, had ample opportunity to extend their lead after Claudio Yacob headed home a Morgan Amalfitano cross in the 42nd minute.
But it was Arsenal who ended the game in the hunt for the points after Wilshere, looking to replace reports of late night smoking with more positive headlines, scored with a deflected first-time shot from 20 yards.
While he has been criticised for lighting up in midweek, the England midfielder will have been happier with the spark he showed in a strong second-half showing.
Had Olivier Giroud been anywhere close to his best he would have settled the issue and put Arsenal two points clear by finishing one of two fine chances teed up by Mesut Ozil and Wilshere.
Albion began the match positively, Saido Berahino combining well with Stephane Sessegnon on his full league debut to free Liam Ridgewell on the left and earn an early corner.
Arsenal cleared the set-piece well and might have had a good break on their hands had the ball fallen to someone quicker than Giroud.
A deflection almost put the hosts ahead just before the quarter-hour mark, Berahino's shot changing course via Mathieu Flamini's leg and needing swift reactions from Wojciech Szczesny.
West Brom gradually took control of the midfield, Yacob and Youssuf Mulumbu proving an effective double act in the central area.
Wilshere was having less joy but came to the fore in 24th minute when he made a neat one-two with Giroud before sending a first-time shot a yard wide.
England manager Roy Hodgson's heart would have been in his mouth when Wilshere hit the deck and stayed there soon after, but his problem proved no worse than an accidental poke in the eye from Yacob.
West Brom were aggrieved when Stephane Sessegnon was blocked as he looked to skip between Mikel Arteta and Kieran Gibbs and nothing was given, though contact did appear to be just outside the penalty area.
Aaron Ramsey, so prolific this season, went close when his low shot through a packed box was well saved by Boaz Myhill but West Brom were enjoying much more of the ball.
Their pressure paid three minutes from the break.
Amalfitano's initial corner was cleared but when Mulumbu produced a sublime piece of control and fed the ball straight back to him, the Frenchman produced a killer cross.
Yacob met it decisively with his head and the Baggies were in front.
There was still time before the whistle for Mulumbu to give Wilshere the runaround with another skilful piece of footwork.
The second half began explosively, with wonderful chances at both ends inside the first three minutes.
The Baggies went first, Berahino galloping forward and making 30 yards before looking for Nicolas Anelka at the far post.
The pass seemed perfect but Anelka made a mess of his finish and got the ball trapped between his feet.
Moments later Arsenal advanced, with Giroud's lay-off finding Wilshere 10 yards out only for a wayward finish to spare West Brom.
The pace barely slowed before Anelka went even closer.
Ridgewell took advantage of a yawning gap on Arsenal's right flank to play in the veteran, who moved towards goal and opened his body only to sidefoot wide of the far post.
Arsenal had a penalty appeal for handball waved away when a Gibbs cross was blocked by Billy Jones, but the full-back appeared to do everything he could to withdraw his arm.
They were level after 63 minutes, with Wilshere the scorer.
Ozil and Giroud were the instigators, with the latter rolling the ball to substitute Tomas Rosicky on the edge of the box.
His one-touch pass sat up for Wilshere, who did not hesitate in unleashing a left-footed shot from 20 yards.
A deflection off Jonas Olsson turned a decent looking effort into an unstoppable one.
Arsenal were buoyed and probably should have taken the lead when a cute chip from Ozil presented Giroud with a delicious chance to volley from 10 yards. He snatched at the shot, though, leaving Ozil to shake his head.
Giroud's struggles continued when a rejuvenated Wilshere picked him out with a glorious ball over the top. This time the combination of a heavy first touch and a brave smothering save by Myhill denied him.
Jones saw a 25-yarder well saved by Szczesny, but it appeared Arsenal's game to win.
Wilshere thought he had a spot-kick when Mulumbu careered into him from behind, but the officials did not agree.