After Brentford hammered Chelsea 4-1 on Saturday, Chelsea manager Thomas Tuchel slammed his "sloppy" side.
Brentford won for the first time against their West London rivals since 1939, moving them closer to relegation safety.
Three minutes into the second half, the Blues seized the lead through Antonio Rudiger, but Brentford answered with three goals in ten minutes.
Brentford's Vitaly Janelt scored twice, Christian Eriksen scored his first goal, and Yoane Wissa added a fourth goal for Thomas Frank's team.
"Nobody saw it coming, especially after going 1-0 up," Tuchel told BBC Sport. "It was out of character for us." We, on the other hand, ceased to defend. We were not sufficiently aware of the threat, were careless in our defense, and were penalized as a result.
"In just ten minutes, they made the most of it." They were fortunate and clinical in scoring three goals. We didn't defend as well as we should have in the Premier League, and we were punished. "
"We lost control for 10 minutes," the German leader admitted. It was a difficult start for us, which isn't unusual after an international break.
He claimed Chelsea players were at ease after scoring the first goal, believing they had already won the game, but they were punished inside 10 minutes.
"We conceded too many shots in general, and we lacked enthusiasm in general." We appeared psychologically exhausted, which is to be expected after traveling the globe, "he remarked.
"We forgot we still had 40 minutes to play after scoring." In my opinion, the fact that we took the lead was well-deserved.
The German claimed that his squad made life difficult for themselves, and that he did not expect them to win the game because they struggled throughout the game, despite taking the lead.
He singled out his defenders, claiming they had quit defending him.