West Ham wasted a chance to seal their Premier League survival as goals from Bryan Mbeumo and Yoane Wissa clinched Brentford's 2-0 victory on Sunday.
David Moyes' side would have been guaranteed to avoid relegation with a victory in west London.
But Mbeumo and Wissa netted in the first half to leave the Hammers still needing one win from their last two games to be sure of staying up.
West Ham are six points clear of third bottom Leeds, who have just two matches left. However, second bottom Leicester would move within four points of the east Londoners if they beat Liverpool on Monday.
With games against relegation rivals Leeds and Leicester to come in their remaining fixtures this was a missed opportunity for West Ham to put their lingering relegation fears to bed.
West Ham are dreaming of a first major trophy since the 1980 FA Cup after beating AZ Alkmaar 2-1 in the Europa Conference League semi-final first leg on Thursday.
But they have now only won one of the seven top-flight matches that have come within three days of them playing in Europe this season.
Moyes had made nine changes with Thursday's second leg at Alkmaar looming.
Declan Rice and Jarrod Bowen dropped to the bench, with Michail Antonio missing out due to a calf injury.
The gamble backfired and Brentford's lively start was rewarded in the 20th minute as a flowing move cut through the West Ham defence.
Mathias Jensen's pin-point pass teed up Mbeumo and he caressed a cool finish past Lukasz Fabianski.
Brentford had lost just once when opening the scoring this season, while West Ham had only one victory when conceding the first goal.
There looked little chance of those sequences reversing as Brentford kept up the pressure.
Damsgaard spotted Aaron Hickey's run into the area and the defender squared for Wissa, whose low strike was saved by Fabianski.
It was a warning West Ham failed to heed as Wissa doubled the Bees' lead in the 43rd minute.
Jensen's long throw was flicked on by Ben Mee and Wissa headed powerfully past Fabianski.
Danny Ings' shot was pushed away for a corner by David Raya in a rare moment of menace from West Ham.
Wissa fired wide after a sloppy mistake from Tomas Soucek that summed up West Ham's lethargic display.
Mikkel Damsgaard should have made it three for Brentford but he volleyed over after Jensen's corner was flicked on by Mee.
West Ham were denied a lifeline when Ings' goal was chalked off for a handball by Divin Mubama.
smg/cw
