Champions League-chasing Newcastle capitalised on poor West Ham defending to hit five goals at London Stadium and pile the pressure on Hammers manager David Moyes.
Callum Wilson and Joelinton put the visitors two ahead inside 15 minutes, before Kurt Zouma pulled one back.
But blunders by Nayef Aguerd and Lukasz Fabianski allowed Wilson to double his tally and Alexander Isak to add a fourth, with Joelinton making it five in stoppage time.
Defeat leaves West Ham outside of the relegation zone on goal difference.
Moyes’ side are one of four teams on 27 points, alongside Everton, Nottingham Forest and 18th-place Bournemouth.
Newcastle remain third and are now three points clear of fifth-placed Tottenham with a game in hand, following a fourth successive win for Eddie Howe’s side.
Hapless Hammers taken apart
While there have been a remarkable 13 managerial changes in the Premier League this season, Moyes has managed to remain in the West Ham dugout – however the Hammers’ abysmal defending here has made his position even more tenuous.
After starting well – a low cross from Jarrod Bowen forcing Bruno Guimaraes to turn the ball onto his own post inside the first minute – the hosts were responsible for their own downfall.
For the opener, Thilo Kehrer headed a deep cross behind under no pressure. The resulting corner was half-cleared and Allan Saint-Maximin’s cross found Wilson unmarked 12 yards out to head in – and the lapses steadily got worse for the home defence.
The second saw a single Fabian Schar long ball beat the whole backline, with Zouma failing to track the run of Joelinton while Emerson did not step up with his fellow defenders to play the Brazilian offside.
Joelinton rounded Fabianski to score and though the goal was initially flagged offside it was allowed following a VAR check.
West Ham briefly woke up and pulled one back when Nick Pope was caught under a Bowen corner, allowing Zouma to powerfully head in and give some hope to the home fans.
But seconds into the second half Aguerd dawdled on a rolled ball from Fabianski, allowing Jacob Murphy to steal the ball and square for a Wilson tap-in.
The defensive shambles coup de grace was saved for the fourth as the Polish keeper rushed out of his goal and miscontrolled a long ball, allowing Isak to lob into an empty net.
By the final whistle London Stadium was half-empty, with Moyes left looking nervously over his shoulder.
