Goals from Marcus Rashford and Ander Herrera secured a 2-0 win for the Red Devils at Old Trafford, which blew open the title race as second-placed Tottenham now trail leaders Chelsea by just four points.
United, meanwhile, remain in the hunt to secure a Champions League spot as the win over the Blues - who sacked Mourinho in December 2015 - takes the club to within four points of fourth-placed Manchester City, who have played a game more than their fierce rivals.
Mourinho's side lost their previous two encounters against Chelsea this season, with the last meeting in March seeing a section of the Chelsea fans call the Portuguese "Judas".
But the United manager insisted on Sunday that beating his former side gives him no extra joy than beating any other team in the Premier League, but conceded the victory was important for the Red Devils' ambition to play in Europe's premier competition next term.
Speaking to BBC Sport's Match of the Day, Mourinho said: "Chelsea are the best counter attacking team in the country and we controlled them very well.
"I'm really happy with the boys. I’m happy - not because it’s Chelsea, it’s because we need these three points.
"I don’t feel extra joy at beating Chelsea - we beat the leader. It doesn’t matter if the leader is Chelsea or another - we beat them convincingly.
"Nobody can doubt our credit to win the game."