West Ham won for the first time under David Moyes as Marko Arnautovic’s first goal for the club proved enough to beat a disjointed Chelsea at London Stadium.
The Hammers scored the only goal after just six minutes when Arnautovic curled a deft strike into the bottom corner after exchanging passes with Manuel Lanzini on the edge of the area.
Chelsea responded well before the break but were repelled by an organised West Ham defence and two solid saves from Adrian, retaining his spot in place of the dropped Joe Hart.
Both sides became increasingly ragged in the second half but West Ham desperately held on, with Chelsea striker Alvaro Morata firing wide when clean through late on.
Despite victory, the hosts remain in the bottom three, though they have drawn level on points with 17th-placed West Brom, who face fellow strugglers Swansea at 15:00 GMT.
Defeat means champions Chelsea will finish the weekend 14 points behind leaders Manchester City if Pep Guardiola’s side beat rivals Manchester United on Sunday.
The Moyes revival
Having ultimately failed to hang on in a vastly improved performance against Manchester City last weekend, West Ham took the next step in proving they could be revitalised under Moyes by this time beating superior opposition.
Their new endeavour was epitomised by Arnautovic, the often frustrating Austria international exchanging positions with his fellow forwards to routinely test Chelsea’s defence.
When makeshift centre-forward Michail Antonio drifted out right early on, Arnautovic cleverly moved inside, collecting Antonio’s pass and playing a quick one-two with Lanzini to leave Andreas Christensen behind, before calmly finishing low past Thibaut Courtois.
He remained a threat even when West Ham dropped deeper and was denied a decent penalty shout when he tried to go past Christensen and the ball hit the Danish defender’s outstretched hand.
At the other end, the Hammers showed greater resolve in defence, largely due to Moyes’ organisation of the central back three and wing backs, with Arthur Masuaku particularly impressive down the left flank.
It could also be a result of Adrian’s more measured presence in goal, exuding more calm to his defence perhaps than the erratic Hart, who could not play against his parent club last week and has now lost his place.
Whatever the main reason, Moyes will surely stick with Adrian going forward and England’s number one Hart could find himself short of first-team football before next summer’s World Cup.
The next test for West Ham is to replicate these performances against the teams around them and drag themselves away from danger.
Is Chelsea’s title defence over?
Even before the halfway mark in the season, it already looks like a second successive Premier League title is beyond Chelsea, who trail the imperious Manchester City by 11 points with the leaders still to play this weekend.
Antonio Conte’s side have now dropped 16 points in as many games, having dropped just 21 in the whole of last season.
As with defeats by Burnley and Crystal Palace, they were poor against less-gifted opposition and the Blues attack was largely innocuous throughout.
Adrian made two fine saves low to his left to keep out N’Golo Kante and David Zappacosta, but both efforts were somewhat speculative and Eden Hazard displayed none of his recent stellar form as he was unable to exploit West Ham’s deep line.
It took a momentary lapse in concentration by Masuaku to create Chelsea’s best chance, as the wing-back played Morata onside only for the Spain striker to pull his shot wide, before Hazard struck over in the closing stages.
Nothing Chelsea did was particularly bad, but neither was it that inspiring – a microcosm of a uneven season in which they look set to be left fighting for second at best.