Eden Hazard's 18th goal of the season in the first half at Stamford Bridge ensured Chelsea moved 10 points clear of Arsenal at the top of the table with six games remaining.
The runaway leaders were not at their best, but Hazard's strike ensured a positive result against Arsenal next weekend would leave them just one win from the title and Chelsea manager Mourinho was able to reflect on another job well done.
He told the BBC: "Six games to play, three at home three away. Every game is difficult, every team needs points. But our situation is very good.
"It was difficult but less than you think. We prepared for the game to be like this. It was the game we wanted and expected. Control their direct football to [Marouane] Fellaini and control the wingers from making crosses on the inside foot.
"When we know [Wayne] Rooney plays in midfield we control his progression into the box. Control set-pieces and don't give away direct free-kicks as they have three specialists. Wait for a mistake and score a goal.
"It was what we wanted it to be. We are happy because the work we did in the week was what happened here.
"I feel we are almost there but there are no almosts in football. We need eight points to be champions. It is pure mathematics."
Mourinho was puzzled that United goalkeeper David de Gea was not sent off for handling just outside the penalty area in the first half, which the officials did not pick up on.
However, the former Real Madrid coach felt referee Mike Dean was right to book Ander Herrera for diving deep into stoppage time when the midfielder claimed he had been upended by Gary Cahill in the penalty area.
He said: "De Gea should see red because he had a handball outside the box. That is the only situation where he can speak.
"Apart from that the referee did a good job. [With the Herrera incident] If it is Chelsea player nobody speak about anything else but diving for a week."
