Toluwani Lasisi
Joao Pedro, Pedro Neto, Enzo Fernandez, Moises Caicedo and Trevoh Chalobah were on target on Friday as the Blues claimed their first win of the season.
As they painted the sky blue, however, they made it successive losses for their hosts in the largely one-sided derby.
In what would otherwise have been bad news for the winners, England forward Palmer was replaced by teenager Estevao Willian as a precaution after pulling up in the build-up to the game.
Chelsea yet 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 to claim crosses from goalkeeper Mads Hermansen 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.
