Chelsea overcame Cole Palmer’s injury in the warm-up and the shock of conceding an early goal to thrash West Ham at London Stadium.
Joao Pedro, Pedro Neto, Enzo Fernandez, Moises Caicedo and Trevoh Chalobah were on target as the Blues claimed their first win of the season – and made it successive losses for their hosts in a largely one-sided derby.
England forward Palmer was replaced by teenager Estevao Willian as a precaution after pulling up in the build-up to the game.
Chelsea suffered another blow when the 18-year-old Brazilian’s backheel was cut out in the sixth minute and Lucas Paqueta strode forward before smashing home a stunning, swerving effort into the net.
But Estevao settled down to sparkle as compatriot Joao Pedro levelled nine minutes later through a close-range header.
A video assistant referee (VAR) check then ruled out West Ham’s last positive action in the game as defender Jean-Clair Todibo was judged to be marginally offside before crossing to set up Niclas Fullkrug to finish.
Neto volleyed Chelsea ahead in the 23rd minute and Fernandez tapped home Estevao’s cross 11 minutes later.
There were a smattering of boos at half-time from the Hammers faithful, but it got worse for manager Graham Potter against his former club.
After Fernandez missed a good chance early in the second half, Caicedo and Chalobah both scored from corners after two weak attempts by goalkeeper Mads Hermansen to claim crosses on his home debut.
The stands emptied after those fourth and fifth goals in the space of four minutes as angry Hammers fans showed their dissent in the club’s first home game of the season, which followed a 3-0 loss at newly promoted Sunderland on the opening day.
West Ham are now without a win in six home matches and eight goals is the most they have conceded across their two opening games of a top-flight season.
West Ham analysis: Problems pile up for Potter’s team
One of the loudest cheers from the home support came in second-half stoppage time when Hermansen claimed a cross.
Of course they were ironic cheers from those that remained in the stadium, after a mass exodus began around the 54th-minute mark when Caicedo struck Chelsea’s fourth goal after a mistake from their keeper, a £20m summer signing from relegated Leicester City.
This was not the fresh start either Hermansen, or the wider squad, will have wanted.
Three of the Chelsea goals came from corners, with blame also likely to fall at the feet of West Ham’s outfield players.
An example was how Chelsea’s 5ft 9in left-back Marc Cucurella managed to flick on a corner, setting up Joao Pedro’s equaliser, against a team playing with three centre-backs.
There was another moment at the end of the first half when midfielders Fernandez and Caicedo were allowed to play six or seven short passes between each other, without being closed down.
That signalled the first sign of discontent for a side who have gone from having a fearsome home atmosphere to becoming an easy place to visit.
There is pressure on the players, manager and owner to put things right after Julen Lopetegui was sacked in January after just 22 matches.
However, Potter has a worse record than his predecessor, earning less than a point per game in his first 21 league fixtures.
