Head coach Graham Potter has put Chelsea's 2-1 defeat to Fulham on Thursday evening down to a number of individual errors.
Chelsea went into the West London derby at Craven Cottage with the opportunity to close the gap on the top four in the Premier League standings to seven points.
However, Potter watched the Blues succumb to their seventh loss in 10 games as Willian and Carlos Vinicius got on the scoresheet for the home side.
Chelsea had got back on level terms through Kalidou Koulibaly early in the second half, but a straight red card handed to debutant Joao Felix changed the game.
The studs-up challenge on Kenny Tete overshadowed what had been an encouraging performance from a player who was only confirmed as a Chelsea player on Wednesday lunchtime.
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While Chelsea also produced a vastly-improved display in comparison to their 4-0 defeat at Manchester City in the FA Cup, Potter acknowledged that he was disappointed with the manner of Fulham's two strikes.
Poor decision-making from Lewis Hall and an indecisive clearance from Trevoh Chalobah contributed to Willian putting the Cottagers ahead with a deflected shot.
Meanwhile, Kepa Arrizabalaga was caught out of position with a cross for Fulham's second, handing Vinicius the chance to head into an empty net at the back post.
Speaking to BT Sport, Potter said: "I think we controlled the game early, won the ball back high created some opportunities, maybe missed the last pass. We made a couple of mistakes for their goal.
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"Second half, I think we responded well and then the red card changes the game. Makes it a little more difficult for us, I thought the application when we went down to 10 was really good. Disappointed with the goal because I think we could do better and that is what cost us."
When quizzed on Felix's red card, Potter admitted that the mistimed challenge and subsequent three-match ban which will now follow was "doubling disappointing".
The Englishman added: "It was a forward's tackle, there was no malice in it but I understand why it was a red. It is another blow the hits keep coming at the moment.
"He was really good you could see his quality in the game so it is doubly disappointing for us."
Chelsea remain in 10th position in the table and return to action at home to Crystal Palace on Sunday afternoon.
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