Andy Carroll's dramatic double lifted West Ham out of the relegation zone, as the Hammers were trailing fellow strugglers West Brom until two goals from their towering striker -- the second deep in stoppage time -- secured a 2-1 win.
James McClean had given the Baggies a first-half lead, but Carroll equalised with a trademark header and then buried an angled shot to leave the West Brom still languishing in the bottom three.
Albion boss Alan Pardew, still without a win from eight matches in charge, had wanted the Premier League to postpone this match as it came just two days after a gruelling 1-1 draw with Arsenal.
He is unlikely to have changed his mind after West Brom's winless streak was stretched to 20 matches.
Seven of Albion's weary starters against the Gunners kept their places, with Jake Livermore a late replacement for Matty Phillips who felt his hamstring during the warm-up.
David Moyes' Hammers, by contrast, had enjoyed a week off having not played since Boxing Day, although they too will feel the pinch with their rearranged trip to Tottenham coming just 48 hours later.
Salomon Rondon, one of those four changes from the Arsenal game, almost gave West Brom an early lead when he spun away from Angelo Ogbonna and, as Winston Reid hesitated, lofted the ball over Adrian and onto the roof of the net.
The visitors opened the scoring, with only their sixth goal on the road this season, on the half hour when McClean cut inside from the left.
He waltzed past Reid's weak challenge and, from the edge of the box, hit a hopeful shot which clipped the heel of Pedro Obiang and looped over Adrian into the net.
It was the Irish midfielder's first goal of the season, and in fact the first he had scored since a 4-2 win over the same opposition in September 2016.
Hammers forward Manuel Lanzini was denied by Ben Foster just before a half-time whistle was greeted with boos from the home supporters.
After the interval Carroll slid in to meet Marko Arnautovic's cross but could only guide the ball over the crossbar.
But Carroll made no mistake just before the hour mark, leaping above Kieran Gibbs and Jonny Evans to thump a header home from Aaron Cresswell's cross.
West Ham were indebted to Ogbonna with 15 minutes left when he chased down sub Oliver Burke from the halfway line and slid in to make a goal-saving challenge in the area to preserve a point.
And in the fourth minute of stoppage time Arnautovic swept one final ball across goal and Carroll slotted in from the angle to secure a much-needed win.