Marko Arnautovic's sixth minute strike, his first for the club, was enough to give West Ham all three points in an impressive display.
Marko on the Mark
From the first whistle, it was clear Chelsea were going to be in for a tough day as they looked sloppy and invited pressure on in the early stages. That early pressure for West Ham paid off as Marko Arnautovic was able to find some space in the box after a neat 1-2, and curl his effort past Thibaut Courtois.
The hosts looked comfortable from the moment they kicked off and the early goal was just what they needed after a heartbreaking loss to Manchester City last weekend.
Chelsea's first real chance didn't arrive until the 22nd minute when Cesc Fabregas' cross was headed down to the feet of Eden Hazard, who fired a fierce volley across the face of goal, but no one could get the important touch.
The visitors continued to push and forced Adrian into a quick succession of saves on the half hour mark. N'Golo Kante and Davide Zappacosta both had low driven efforts parried away by the goalkeeper, keeping it at 1-0.
No answers for the Blues
The second half began with some controversy as Arnautovic's flicked ball struck the hand of Andreas Christensen, but the referee waved away the protests. An accidental handball that was rightfully not awarded.
Chelsea could not get anything going and had to wait until the final ten minutes for a clear cut opportunity. Kante's threaded pass found Alvaro Morata with plenty of space inside the box, but the striker pulled his effort wide of the near post. A golden chance missed for the visitors would be followed up by a half-chance moments later as Hazard's shot from outside the area was sliced high and wide.
Despite being on the backfoot for the majority of the second half, West Ham did well to prevent clean looks at goal and kept Antonio Conte's side out.
West Ham would run out 1-0 winners, grabbing the early goal and defending well against the visitors. Chelsea on the other hand will be extremely disappointed with their lackluster performance. By the end of the weekend, Chelsea could be staring at a 14-point gap between themselves and top spot in the Premier League, while West Ham's three points lift them up to 18th.