Lucas Paqueta and Michail Antonio struck second-half goals as 10-man West Ham beat Chelsea 3-1 in an action-packed derby at the London Stadium.
The Hammers made the perfect start when £30m summer signing James Ward-Prowse capped his debut with an assist inside seven minutes.
Nayef Aguerd was the beneficiary as he rose highest to head the former Southampton midfielder’s right-wing corner past Robert Sanchez.
Chelsea responded and deservedly levelled when 19-year-old Carney Chukwuemeka rifled a superb solo strike into the far corner for his first senior goal just shy of the half hour mark.
The lively Raheem Sterling then earned Chelsea a penalty two minutes before half-time, but Enzo Fernandez’s low spot-kick was well saved by Alphonse Areola.
The pattern of Blues dominance threatened to continue following the break, but it was the hosts who stole in front when Ward-Prowse chalked up a second assist, releasing Antonio to surge free and thunder a sublime, low strike into the far corner.
Chelsea turned to British record signing, Moises Caicedo as he made his debut from the bench and their hopes appeared to be further boosted when Aguerd was sent off for a second bookable offence 23 minutes from time.
However, West Ham defended for their lives and then sealed the points when Caicedo brought down Emerson, allowing Paqueta to convert a stoppage-time penalty.
The result leaves Mauricio Pochettino still waiting for his first competitive win in charge of the Blues and moves the Hammers up to sixth spot in the fledgling standings.
Next up, Chelsea host top-flight newcomers, Luton Town on Friday night while winless West Ham visit high-flying Brighton on Saturday.