Tottenham captain Son Heung-min called Spurs' latest defeat "unacceptable" and said his fellow players "need to take responsibility" after they dropped points from a winning position for a fifth consecutive game.
Ange Postecoglou's men deservedly took an early lead at home to West Ham on Thursday night but were ultimately beaten 2-1 following a second-half comeback.
No team has dropped more points from winning positions in the Premier League this season than Tottenham, who have relinquished 16.
And Spurs' run of five matches without a win has caused the Lilywhites to drop from first, with a five-point lead at the top of the table, to fifth.
"[Whether we] deserved better or not means nothing - we lost the game. It is unacceptable," Son told Amazon Prime.
"As players [we] should take responsibility. Attacking players should [especially] feel responsibility because we had chances to kill the game."
Tottenham hit the post through Giovani Lo Celso's deflected cross in the first half, while Richarlison had a fine chance to restore the hosts' lead in the second period but nodded a close-ranger header wide.
Ultimately, though, West Ham were clinical and Tottenham lacked a ruthless touch despite racking up 23 shots.
"If you dominate a game of football you have to turn it into something meaningful and we didn't," Postecoglou added on BBC Match of the Day.
"We let ourselves down when we should have won the games [we have taken the lead in] comfortably."
Tottenham made a brilliant start to the Premier League season, winning eight of their first 10 matches.
But they last tasted victory in October and have now lost three consecutive league home fixtures for the first time since September 2008, when they were managed by Juande Ramos.
After defeats by Chelsea, Wolves, Aston Villa and West Ham - all having taken the lead - talk of a title push is turning into worries of another finish outside the top four.
"The challenges are there. It is no good feeling sorry for ourselves," said Postecoglou. "We still have a long way to go as a team and today shows that.
"In a game of football if you don't put those chances away teams are always going to have the opportunity to punish you. In both boxes we were nowhere near where we need to be."
Tottenham face Newcastle in the Premier League in their next match on Sunday.
