Mauricio Pochettino felt Tottenham lacked solidity as they surrendered a one-goal lead to lose 2-1 against Southampton on Sunday.
Steven Davis struck twice at White Hart Lane to overturn Son Heung-min's early goal, leaving Spurs winless in their last three games.
They have now lost 20 points when leading - more than any other Premier League side - and Pochettino was disappointed with his side's defending.
"In the first half we played very well, and it's true we went out to win the game," he said.
"We created the better chances and had the possession, but when we needed to be more solid and show more consistency, we lacked it today. It is disappointing but we are still fighting."
Tottenham's title challenge ended in a draw at Stamford Bridge last Monday, but Pochettino rejected the suggestion the result had an impact on their performance against his former club.
He said: "We started the game very well and there's nothing to say about that.
"I was a little bit disappointed with how we conceded the first goal and then in the second half we had control.
"They had a very quick player up-front but only had two shots on target and they scored two. This is football and we congratulate them."