West Ham came from a goal behind to beat AZ Alkmaar 2-1 in the first leg of the Europa Conference League semi-final at the London Stadium.
Dutch side Alkmaar frustrated the home team in the first half and took a surprise lead when Tijjani Reijnders beat Alphonse Areola from distance.
But West Ham – bidding to reach a first European final in 47 years – turned the tie around in the second half thanks to Said Benrahma’s penalty and Michail Antonio’s goal.
David Moyes’ side have all but secured their Premier League survival and are looking to end the season by winning a first European trophy since 1965.
West Ham will look to consolidate their one-goal advantage and book a place in the Europa Conference League final when they travel to the Netherlands next Thursday.
In the other semi-final tie, Swiss side Basel scored an injury-time winner to beat Italian outfit Fiorentina 2-1.
West Ham clinched a crucial victory over Manchester United prior to the visit of AZ Alkmaar to move seven points above the drop zone with three games remaining.
But it was not immediately obvious that that win had given confidence to the Hammers squad, who struggled to create any clear-cut chances during a frustrating first half for the hosts.
Benrahma had West Ham’s best chance of the half when he cut in from the left and curled a shot that would have crept into the bottom corner had it not been for a fantastic save by Mathew Ryan.
If anything, Alkmaar – who are fourth in the Eredivisie – were on top, with West Ham growing frustrated by what they perceived to be time-wasting tactics.
The London Stadium was left stunned as Alkmaar took the lead shortly before half-time; Reijnders leading a counter-attack and then finishing past Areola, who ought to have done better.
AZ Alkmaar continued to frustrate West Ham in the second half until the hosts were awarded a penalty as goalkeeper Ryan essentially punched Bowen as he attempted a header.
Benrahma converted the spot-kick and from that moment the momentum was with the Hammers, who scored again just eight minutes later through Antonio, who poked home following a goalmouth scramble.
It could have been even better for West Ham, who threatened late on through Benrahma and substitute Danny Ings, but Moyes had to settle for a 2-1 win ahead of the return leg in Holland.
There was a second-half comeback in the other Europa Conference League semi-final as Basel recovered from Arthur Cabral’s opener to win 2-1 thanks to goals from Andy Diouf and Zeki Amdouni.