Antonio Conte accepted that retaining the Premier League title is "impossible" after West Ham inflicted Chelsea's fourth defeat in 16 matches this season.
Marko Arnautovic gave the Hammers the lead after just six minutes and that proved to be the crucial goal, as David Moyes' men held on for a 1-0 London derby win.
Chelsea were afforded a lot of the ball throughout and put their hosts under significant pressure, but they struggled to find a way through West Ham's packed defence.
And that result leaves them 11 points behind pacesetters Manchester City, a figure which could be increased after Sunday's Manchester derby.
Conte says after a fourth defeat in 16 games is it 'impossible to think you are in the title race'. #WHUCHE— Chelsea FC (@ChelseaFC) December 9, 2017
"To talk about the title race after a defeat I think is a bit strange," Conte told reporters in his post-match news conference.
"Especially as this is the fourth defeat this season in 16 games. When you have this task, it is impossible to think that you are in the title race.
"It is impossible. My experience is this, if you want to stay in the race for the title, in the first part of the season you can lose once, twice."
For Conte, there was no doubt about what Chelsea's problems were, ruing their wastefulness after starting "badly".
He said: "We lost the game against West Ham, it was very because we started badly and conceded this goal and it was difficult to come back. I saw the same game against Manchester City, where Manchester City attacked for the whole game against the whole team behind the ball.
"But City found a way to score. Instead we created the chances but didn't take them. Now we are talking about the defeat. Many players were tired. It is normal when you play in a few days. We started our pre-season with the same players, a lot are playing almost always, and for sure you have to pay something for this."