After being outwitted by City boss Pep Guardiola, the Special One pointed the finger at players who bottled it, saying they could not handle the pressure.
Mourinho hauled off Jesse Lingard and Henrikh Mkhitaryan at half-time but admitted he wished he could have taken off more.
He said: “I didn’t want to make two changes after 20 minutes and destroy them.
“But if it was a sport like basketball or this kind of stuff, then I would have done more.
“I made two at half-time but it could have been three. My boys felt the dimension of the game.
“The derby, Man United, Man City, the focus, the attention, I felt that some of the guys felt it.
“We had individuals who did not give us what we were expecting — three, four or five players.
“They didn’t give me what I want. And therefore it’s my fault as I’m the manager, it’s my choice.
“But maybe in the next big game I know who can accept the dimension of the game — which is very important.”
The Special One added: “It has nothing to do with experience or age because we put on the kid Marcus Rashford in the second half and it looks like he is playing Under-18s v Salford City.
“Everyone feels it in different ways and it is difficult to predict.
“When you work with them for one month, two months, three months or four months then you learn.”