Maurizio Sarri knew Chelsea had "problems" before they were defeated 3-1 by Tottenham in Saturday's London derby.
Sarri suffered his first defeat in the Premier League as Blues boss, with Spurs flying out of the blocks with goals through Dele Alli and Harry Kane.
Son Heung-min's brilliant 54th-minute solo effort put the result beyond doubt, with Olivier Giroud's late header coming as scant consolation.
Before the match, Sarri voiced concerns over his players' mentality due to slow starts in recent games – words he was disappointed to see vindicated at Wembley.
"I knew very well that we had some problems. Today we have seen that we have problems. We have to work, we have to improve," he told BT Sport.
"We were against a very strong team, especially when they can use very short counter-attacks. At the beginning of the match we lost a lot of balls in our half and it was a very big problem.
"It was clear. I think in the last two or three matches that we had a problem at the beginning of the match. Today the difference is only the opponent.
"We had a lot of problems. Physically we didn't do a very good performance, technically the same. We were not compact for 90 minutes.
"I think that we had a lot of problems and we have to work on a lot of the actions."
When the score was 1-0, Tottenham defender Juan Foyth was fortunate not to be penalised for a clumsy challenge on Eden Hazard in the penalty area, but Sarri was in no mood to look for excuses.
"I think that it is not important," he added. "I have to think about the other 93 minutes. It's not important if the penalty was a penalty or not."