Tomas Rosicky scored twice as a 10-man Arsenal side withstood a West Brom challenge to move ahead Chelsea into fourth place in the Premier League.
Rosicky cleared a Claudio Yacob effort off the line early in the game before putting Arsenal ahead himself in the 20th minute.
Rosicky struck again when drilling the ball into the bottom corner of the net in the 50th minute.
James Morrison converted a penalty as Per Mertesacker was sent off for a foul on Shane Long, but Arsenal held firm.
The Gunners go a point clear of Chelsea in fourth spot, and are one point behind Tottenham.