Marko Arnautovic scored the only goal, as West Ham beat Chelsea 1-0 in Saturday’s early kick-off.
The Austrian forward netted after only six minutes, to condemn the champions to their first defeat in seven Premier League matches.
It was the first win charge of the Hammers for David Moyes, who again dropped Joe Hart for Adrian in goal.
Adrian justified his selection with fine first-half saves from N’Golo Kante and Davide Zappacosta.
The result means Chelsea now have 32 points from 16 fixtures.
The gap between the Blues and the Manchester teams could be bigger after Sunday’s games.