Chelsea took a huge step towards securing a Champions League spot as Timo Werner's first goal since February helped Thomas Tuchel's side beat top four rivals West Ham.
Werner, who has struggled to make a significant impact since joining for £47m last summer, started and finished the move that settled a tightly-fought game.
The Germany forward fired home from Ben Chilwell's cross after a well-worked move involving Christian Pulisic, Werner's sixth Premier League goal since arriving from RB Leipzig.
West Ham struggled to create chances and finished the game with 10 men after Fabian Balbuena was shown a straight red card in the 81st minute after catching Chilwell's leg with his follow through while making a clearance.
Referee Chris Kavanagh watched a replay on the pitchside monitor before dismissing the Paraguay defender.
The result leaves Tuchel's side in fourth place, three clear of West Ham and four clear of Liverpool.
"The win was well deserved. We played amazing in the first half," Tuchel said after the game.
"We did not come out of the dressing room with the same intensity as in the first half. We suffered a bit with their intensity, but I think we deserved to win. It's a very important win."