Goals from Juan Mata and Anthony Martial secured the victory that also stretched United's unbeaten league run to 16 matches, with their last defeat coming in the 4-0 thrashing by Chelsea at Stamford Bridge.
Mourinho has been quick to highlight what he considers to be a much more defensive, counter-attacking approach from his old club this season and he believes that their style of play makes it unlikely that they will be caught at the top of the table.
"We needed to win," he said, as quoted by BBC Sport. "Sixteen games unbeaten is an amazing record but it would be the perfect record with two or three fewer draws at home.
"It was a difficult match and a very important win for us. We are not a team scoring lots of goals so it is important to keep the clean sheets. I am really happy with the performance.
"In the 10-15 minutes before the goal we were playing in a brilliant way. The goal had to come.
"Chelsea are very good defensive team. They defend very well and with lots of players and I think in this situation a very defensive team wins the title with counter-attack goals and set-pieces goals, so I don't think they will let it slip but football is football."
Mata admits that United feared they could be held to what would have been a seventh draw in 10 home games as they contrived to miss a number of chances before finally taking the lead on 32 minutes.
The Spain international felt their display was otherwise strong and would not rule out the prospect of chasing down Chelsea.
"When you play good football and get the three points it is a step forward but we need to keep going," he said. "It was a convincing performance and we are very happy today.
"It started to feel like it was one of those games again. Their keeper saved every chance but then the goal came and after that it was more comfortable for us. We are going in the right direction.
"It is very, very difficult. First of all is to get into the top four. We have been winning games but not going higher in the table. We want to go higher and higher. We never know where we will finish."