Jose Mourinho felt "incredible defensive mistakes" were to blame for Manchester United's 4-0 thrashing against Chelsea at Stamford Bridge on Sunday.
The Portuguese manager was returning to face Chelsea for the first time since leaving last December, and things started badly for United with Pedro opening the scoring after just 30 seconds.
Gary Cahill made it 2-0 when the ball ricocheted off Ander Herrera from a corner, while both Eden Hazard and N'Golo Kante dribbled past Chris Smalling to add to the hosts' tally after the restart.
Mourinho felt the early goal completely changed the match and was frustrated to see his team punished on the counter-attack.
"The first minute you analyse the goal and you see immediately what happened. We made incredible defensive mistakes. Individual defensive mistakes and you pay for that," he told Sky Sports.
"If you equalise or score the 2-1 after the 2-0 you have a big chance because in terms of football the team was quite comfortable.
"With a strategy you cannot [let the opponent] score in the first minute and after that, the game changed completely. [The gameplan] goes out of the window, but we were coming to have an offensive approach.
"We wanted to create chances, we wanted to score goals. We showed that immediately after the 1-0 when we had chances and positions. I think at the end [Thibaut] Courtois had more saves than [David] De Gea.
"I told the players we should take the risk in the second half knowing they are very good on the counter-attack, but if we scored a goal like we almost did the game could be completely different, but it's one of those days where we give the advantage to the opponent.
"They were winning 2-0 after 20-25 minutes. After that they played well, they were defensively compact and they used what they possess best, which is the counter-attack.
"In the second half we played with [Marcus] Rashford through the middle to create more mobility from Zlatan's [Ibrahimovic] position.
"We played with two midfield players we had no problems at all, we had control of the game, but the control is a bit dangerous because Chelsea has great players on the counter-attack and they were just waiting for that."
Following the fourth goal the Chelsea support chanted Mourinho's name, and the manager said he got the sort of reception he was expecting.
He added: "I was not expecting anything different. The people inside of the tunnel are friends, and the crowd behaved in a normal way."