Despite seeing Lucas Paquetá put the Hammers ahead with a samba-style strike, the visitors quickly bounced back as they romped to a free-wheeling 5-1 victory.
“It’s been a tough week,” grimaced former Blues boss Graham Potter, whose sorry Hammers side – having suffered a three-goal defeat at the Stadium of Light six days earlier – sit rock-bottom of the Premier League after conceding eight times across their opening two matches.
“We went to Sunderland filled with positivity but got smashed on the nose and now we’ve gone and defended cheaply against a top team full of talented players. We need to drastically improve.”
Paquetá spectacularly gave the Hammers a sixth-minute lead after compatriot Estêvão - a late replacement for Cole Palmer (groin) – casually lost possession on the halfway line.
Picking up the pieces, El Hadji Malick Diouf found West Ham’s own boy from Brazil, who galloped forward before unleashing an unstoppable bending, dipping, diagonal 25-yarder that whistled beyond the outstretched right glove of Robert Sánchez and under the keeper’s left-hand angle.
But the Hammers lead did not last long.
On the quarter-hour mark, Pedro Neto floated a corner towards Marc Cucurella, who outjumped Paquetá at the near post and sent a back-header into the goalmouth, where João Pedro climbed between Aaron Wan-Bissaka and Niclas Füllkrug to nod home the equaliser.
Moments later, Füllkrug’s low drive was disallowed after a Video Assistant Referee review ruledJean-Clair Todibo had strayed a mere toecap offside in the build-up and those stray studs would prove decisive.
Midway through the opening period, Trevoh Chalobah outmuscled Paquetá before inviting João Pedro to set up Pedro Neto and, ten minutes later, another incisive raid enabled to Enzo Fernández to slide home Estêvão’s low cut-back.
“We’d got off to a great start but their first goal set the tone for the evening and if you defend like that against a talented side such as Chelsea it becomes impossible,” added Potter, who introduced Callum Wilson and Freddie Potts at the interval.
But within ten minutes of the restart – on a home debut to forget - Mads Hermansen haplessly palmed Fernández’s corner onto the boots of Moisés Caicedo, who lashed the loose ball back past the red-faced £20m summer signing from relegated Leicester City.
Then, on the hour, more calamitous corner chaos allowed Chalobah to prod home João Pedro’s nod-down.
“There’s always disappointment when you concede but tonight it was about the manner of their goals. They were too cheap and too soft. It’s about basic defending,” continued the Hammers head coach, who could so easily have been looking at a tennis score by the final whistle.
“As a manager you’re under pressure all the time in these jobs but I know the territory and what comes with poor results.
“I accept the responsibility but I’m also confident both in myself and my players - they’re honest, they care and I know they all want to do better.”
Potter now faces a midweek Carabao Cup tie at Wolverhampton Wanderers before making the tricky trip to Nottingham Forest on Sunday (2pm).
"We’ve got to look for solutions, stick together and fight,” he said.