Arsenal clinched their place in next season's Champions League with a hard-fought 3-2 victory at the Hawthorns.
The win for Arsene Wenger's side saw them see off the challenge of Tottenham Hotspur who now face an anxious wait for the result of next Saturday's Champions League final between Chelsea and Bayern Munich.
There will be no such issue for Arsenal, after Laurent Koscielny secured a vital three points at the end of a tumultuous campaign.
But the Gunners's win owed much to a number of high-profile errors made by West Brom goalkeeper Marton Fulop.
The goalkeeper, only appearing after the ever-consistent Ben Foster suffered a groin injury in training on Saturday, was at fault for Arsenal's opening goal as Yossi Benayoun was allowed the simplest of chances to poke the ball beyond him and into the empty net.
But two quick goals quickly altered the complexion of the match in West Brom's favour. A driving run by James Morrison found Shane Long in behind the Arsenal defence and the Republic of Ireland striker made no mistake with a low drive into the bottom left-hand corner of the net.
West Brom quickly seized the advantage when Graham Dorrans took the ball away from Koscielny before tucking a low shot beyond Wojciech Szczesny. A further mistake from Fulop allowed Arsenal back into the match on the half-hour mark when Andre Santos hit a vicious shot that squirmed through the goalkeeper's grasp.
And Arsenal claimed victory after the break, when Fulop failed to clear a Robin van Persie corner and Koscielny was on hand to nudge the ball into the net with his right foot.