Antonio Conte conceded Chelsea are out of the title race after their 1-0 defeat at West Ham.
Marko Arnautovic's early goal condemned the Blues to a fourth defeat of the season and left them 11 points adrift of leaders Manchester City.
And boss Conte admitted: "This is the fourth defeat in 16 games. When you have these stats it's impossible to think you are in the title race.
"If you want to stay in the race for the title in the first part of the season you can only lose once or twice."
Chelsea were carved open far too easily with West Ham's first attack in the sixth minute, when Arnautovic played a quick one-two with Manuel Lanzini.
The Austrian nipped in behind Andreas Christensen and, as Cesar Azpilicueta stood off, curled his shot around the defender and keeper Thibaut Courtois.
Chelsea had plenty of time to respond, yet it was a strangely subdued display from a side with six wins from their previous seven outings.
When their clearest chance arrived, six minutes from time, Alvaro Morata snatched at his shot and clipped the side netting.
"Today it was very difficult, our start was bad and it was difficult to come back," added Conte.
"We created chances but didn't take them and now we are talking about a defeat.
"Many of the players were tired. It's normal. We started our pre-season with the same players, a lot of players are playing almost always.
"Today our ideas were not so clear. We made a lot of mistakes from the final pass. We can do better."
Arnautovic, West Ham's £24million club-record signing, was jeered by home fans earlier in the season after some below-par displays but he looks a player reborn under David Moyes.
In fact West Ham looked an entirely different side to the shambles they appeared towards the end of Slaven Bilic's spell in charge as they secured a first win since Moyes took over at the end of October.
Moyes showed he is not one to shy away from tough decisions, and dropping England goalkeeper Joe Hart in a World Cup year was certainly a big call.
But Hart's replacement, Spanish keeper Adrian, justified his selection with fine saves from N'Golo Kante and Davide Zappacosta.
"I thought Adrian played very well," said Moyes. "Joe took the decision really well and gave Adrian plenty of encouragement so I have to praise Joe."
For Moyes, it was also a first home win as a manager in almost a year, having presided over Sunderland's miserable relegation campaign last season.
"All managers need wins. That's the way it is," he added.
"I think coming to the club everyone could see I have had a pretty difficult run of fixtures, but today we did a job, the game plan worked.
"I'm always happy when I win. The best feeling is the Saturday night feeling after a win.
"But then I put my jacket on as I left the dressing room and thought 'oh no, we've got Arsenal in midweek'."