Chelsea boss Antonio Conte took the blame and claimed his side's title chances had been reduced to "50 per cent probability" after defeat by Manchester United.
The Premier League leaders, 10 points clear at the start of the month, are now just four points ahead of Tottenham with six games to play following a 2-0 loss at Old Trafford.
Goals from Marcus Rashford and Ander Herrera condemned the Blues to their latest slip-up as their former manager Jose Mourinho tactically outsmarted his successor Conte.
Conte said: "We didn't play a good game and United deserved to win the game. They showed more desire, more ambition, more motivation to win.
"It is very simple but in this case the fault is of the coach. It means the coach wasn't able to transfer the right concentration, desire, ambition to win this type of game.
"We have to think that there are six finals from now until the end. The league is open and we have a 50 per cent probability to win the league."
Chelsea's immediate attention now switches to the FA Cup but, interestingly, they play in-form Spurs in their semi-final at Wembley next Saturday.
Conte said: "It won't be easy because I think Tottenham now are the best team and they are in great form and they have a lot of enthusiasm. They are feeling the possibility to write the history."
Conte, who won three Serie A titles in charge of Juventus, insisted the pressure of the title battle would not get to him.
He said: "The pressure is normal. I prefer to play for the title instead of 'don't fight for the title and stay calm'. We are lucky to have the pressure.
"We must have great enthusiasm to play these last six games, with patience and a great will to fight."
United's performance was one of their best since Mourinho took charge last summer. Herrera, who effectively shackled dangerman Eden Hazard, set up Rashford's early opener and then added a deflected second after the break.
Mourinho said: "I think it was a special performance because it's also a special opponent.
"I think we played really well, a very solid performance.
"We gave them double problems. We gave them problems when they had the ball because we controlled very well and we gave them problems when we recovered the ball because we were really sharp and fast and aggressive in our transitions.
"So, I am very happy with the performance. Very happy."
The result boosted United's chances of finishing in the top four and continued their long unbeaten run in the Premier League.
Mourinho, who denied he took extra satisfaction in beating his former club, said: "Normally you win the title if you are 22 matches unbeaten and we are struggling to finish top four.
"But it's a great feeling to know that it's difficult for us to lose a match, people fight until the end.
"I think we need a little bit more quality and different qualities in some positions for next the season to make the squad stronger but in terms of character and the human side of the group, I have one of the best groups ever."