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Fornals set up two goals, and Antonio registered a goal and an assist. Jarrod Bowen and Sebastien Haller also scored for West Ham.
The Irons move out of the drop zone with 27 points, while Saints’ 34 points are nine clear of the bottom three.
Michael Obafemi scored Southampton’s goal.
Three things we learned
1. Fornals keeps rising: The ex-Villarreal man went his first 12 Premier League outings without a goal or assist, but now has two goals and five assists after Saturday’s pair of helpers.
2. Inspired Haller returns: The French center forward was absolutely monstrous on Saturday, and it’s not about his goal. Haller won 21 of 33 duels and 14 of those wins came in the air as David Moyes asked a lot of his big man. Haller had two key passes, two shots on target, and completed four of five dribbles. Key man.
3. Saints waste chance to improve UEL stock: Ralph Hasenhuttl‘s men rarely looked ready to prevail in London, with key mistakes from center back Jack Stephens and Alex McCarthy thwarting a chance to go 10th.
Man of the Match: Fornals.
Bowen gave West Ham the lead off a Saints giveaway, as a lively Pablo Fornals sent the ex-Hull man through for a clever chipped finish.
Michail Antonio was a threatening presence and nearly had the Irons up two.
Saints made it 1-1 when Obafemi worked Ward-Prowse’s cutback beyond the reach of Fabianski.
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West Ham reclaimed the advantage before halftime.
Haller got his seventh goal of the season and first since New Year’s Day when he beat Alex McCarthy to Antonio’s cross and deposited the resulting loose ball.
Antonio was rewarded with a goal of his own in the 54th minute, Fornals again assisting a vital marker.Follow @NicholasMendola