Mourinho, sacked by Chelsea last season, could be forgiven for doing everything in his power to beat Antonio Conte's side after suffering two chastening defeats at the hands of the Premier League leaders earlier this season.
The 54-year-old was humiliated on his return to Stamford Bridge in October and took umbrage with Conte's touchline celebrations as Chelsea cruised to a 4-0 win.
Mourinho fared no better when he went back to the Bridge in the FA Cup quarter-finals in March as Chelsea won 1-0 after United midfielder Ander Herrera was sent off.
Adding insult to injury for Mourinho, the self-styled "Special One" was taunted by Chelsea fans who called him "Judas" and chanted "you're not special anymore" following the United manager's touchline row with Conte.
Mourinho, the most successful manager in Chelsea's history, hit back by pointing out that "Judas is number one" in Chelsea's record books.
With fifth-placed United desperately needing a victory this weekend in the battle for Champions League qualification and Chelsea, seven points clear at the top, looking to move a step closer to the title in Conte's first season, the stage is set for a classic encounter.
But Mourinho is trying his best to take the emotion out of the showdown, insisting Sunday's match is like any other.
"You say that word 'emotion'," he said when asked how his emotions differ from the previous meetings.
"For me, it is just a game. One more game. No difference for me."
Asked if there was nothing special about the game, Mourinho: "No, not at all."
United have gone on a 21-match unbeaten league run since losing to Chelsea in October, but a lack of cutting edge has damaged their bid to finish in the top four.
That lack of cutting edge reared its head again on Thursday as Anderlecht snatched a late 1-1 draw in the first leg of their Europa League quarter-final.
Chelsea have had no draining European fixtures to distract them from the Premier League title race this season, giving them a freshness Mourinho says has been beneficial for his former club.
"First of all, some guys are fresh, some guys are tired," the United boss said when asked how the sides compare.
"That's very important in football. But for some reason they are top of the league, it's not just because they are fresh.
"It's also because they have individual quality and they have collective quality.
"They have a certain style of play. They stick to it, they do it very well."