United's latest defeat away at Watford on Sunday was their third successive in all competitions. [EPL game week 5: Roundup]
The slide began with a 1-2 derby defeat against cross-town rivals Manchester City, which was followed by a 0-1 loss against Dutch side Feyenoord in the Europa League.
Mourinho said his side failed to learn the lessons of last Saturday's Manchester derby, after conceding an "incredibly similar" goal to Watford on Sunday.
"What is in my hands is the improvement of the team and the individuals," Mourinho was quoted as saying by The Independent on Sunday.
"To try to stop with the defensive mistakes, and I knew that I had a task. I knew that because, for example, between the first Manchester City goal and this second goal today, you can find an incredible similarit".
"My players, instead of going up to press, they decide to give spa"e," said Mourinh". "We have to improve, no doubt, individually and collectively. And t'at's my j"b."
Mourinho said that United had been the better team in the second half and that that mistake had turned the ga"e. "At 1-1 everyone thought we were going to win the game, and we were showing complete control, intensity and creat"on," he said."
"Obviously after 1-1 that was clearly the tendency of the game. The game was there to win, and never to lose. Their second goal was a mistake, that goes against our plan and our training. Their second goal comes from there, completely against the normal tendency of the "ame."
Mourinho said that there is still a lot of work for his team to do and that his players will have to cope better with the pressure of expectat"on. "I was completely aware this is not a perfect team, that lots of players are not end products, and they can make their own mist"kes," Mourinho added"
"My only doubt was the way they can cope with negative moments, because the negative moments will be always arriving sooner or later. I feel some individuals feel too much pressure and responsibility, but by the collective point of view I only have good things to say about "hem."