Jose Mourinho was left to rue "incredible defensive mistakes" as Manchester United were beaten 4-0 by Chelsea on Super Sunday.
On his return to Stamford Bridge, Mourinho's side endured a terrible start as they fell behind after 30 seconds.
It got worse in the first half as Gary Cahill doubled the advantage, before Eden Hazard and N'Golo Kante added further gloss to the scoreline after the break.
Mourinho told Sky Sports that the opening goal changed the course of the game.
"In the first minute, you analyse the goal and you can see what happened - we made incredible defensive mistakes, individual defensive mistakes and you pay for that," he said.
"After a few seconds you are losing 1-0, then you go close to 1-1, then another defensive mistake and it's 2-0.
"Then you are close to 2-1 and they counter for 3-0, then you are close to 3-1 and they score to make it 4-0. You come with a strategy and you cannot concede a goal the way we did in the first minute, that changed the game."
Defeat stretches United's winless run in the Premier League to three matches after draws with Liverpool and Stoke.
And Mourinho is keen to return to winning ways after a tough run of fixtures concludes with an EFL Cup clash against Manchester City on Wednesday.
"We had a week where we have played two (title) candidates in Liverpool and Chelsea and now the other teams from the top five have to play among themselves, they have to draw and lose the points each," he said.
"We need to win our matches now, which is not easy but we play Burnley, we play Swansea and West Ham and we need to win matches to close the gap."
Mourinho appeared to exchange heated words with Chelsea boss Antonio Conte after the full-time whistle, but he would not elaborate on what was said.
"I am not the kind of guy to share with you things between me and Antonio. It stays between me and him, unless he wants to share it," he said.
On his reception from the home fans at Stamford Bridge, where he won eight trophies over two spells, he said: "I was not expecting anything different and the crowd behaved in the normal way so... nothing wrong."