Two superb goals from Francis Jeffers and Thierry Henry crowned a determined comeback by Arsenal and strengthened their grip at the top of the Premiership.
West Brom now have only one win to their credit in 14 league outings, but they shocked the high-flying Gunners, taking the lead after only three minutes at a packed Hawthorns.
After the break Arsenal, who had lacked punch in the opening 45 minutes, took the game by the scruff of the neck as they sliced open the Albion defence with some fine attacking football.
Struggling Albion's only moment of glory came after Jason Koumas chipped a perfect right-wing corner into the heart of the Gunners defence.
The dangerous Dichio had a free header and he placed his terrific strike past David Seaman to claim his third goal of the season.
The strike from the transfer-listed Dichio failed to lift Albion and the scoreline was level in the 48th minute when a hard left-wing ball took a deflection to fly into the path of Jeffers.
The Â£7million former Everton star kept his cool as he drove a marvellous shot past the helpless Russell Hoult and into the roof of the Albion net.
Albion were always second best in the second half but they were unlucky in the 77th minute when Jason Roberts caught the Arsenal defence flat-footed only to fire his shot against the foot of the far post.
The game was decided with just five minutes left on the clock when Henry banked the all important points for Arsene Wenger's visitors.
The striker pounced on to a poor clearance from Adam Chambers to slot the ball into the back of the empty Albion net with keeper Hoult already committed.