United have drawn five of their last six home games and go into Sunday's Old Trafford showdown on the back of a leggy 1-1 draw at Anderlecht in the first leg of their Europa League quarterfinal.
They are far from ideal conditions in which to be preparing an ambush of the champions-elect, but despite his protestations that it is "just one more game", Mourinho is likely to be highly motivated.
Sacked by Chelsea midway through last season's car-crash title defence, he has had two deeply unpleasant experiences on his two trips to Stamford Bridge this season.
In October, he saw United thrashed 4-0 and made a public show of taking Chelsea manager Antonio Conte to task over his touchline exhortations, accusing the Italian of trying to "humiliate" him.
February's 1-0 FA Cup defeat was a closer affair, but brought with it barracking from the fans who had once sung his name.
In response to their taunts of "Judas!", he raised three fingers - one for each of the Premier League titles he won over his two spells as Chelsea manager.
"When they have somebody that wins four Premier Leagues for them, I become number two," he said after. "Until this moment, 'Judas' is number one."
Mourinho cannot have enjoyed watching the players who seemed to down tools under him thriving under Conte, as typified by the form of Eden Hazard.
Hazard, who played like a ghost under Mourinho last season, will arrive at Old Trafford seeking to reach the milestone of 15 goals in a league campaign for the first time since he signed from Lille in 2012.
For his part, Conte has sought to play down any suggestion of tension between himself and Mourinho.
"I have zero problems (with Mourinho)," he said. "It's only a sporting competition between him and me.
"There is a game of football. I want to try and win with my team. He wants to try and win with his team. It's normal to be at conflict during the game, but only a sporting conflict."
While Chelsea are no longer the free-wheeling team seen in the weeks before Christmas, having gone nine league games without a clean sheet, they boast a formidable record against United.
They are unbeaten in the teams' last 12 encounters, stretching back to a 3-2 home defeat against a side managed by Alex Ferguson in October 2012.
Conte also has the luxury of being able to pick from a full squad, after Victor Moses made his return from a toe problem in last weekend's 3-1 victory at Bournemouth.
Life is nowhere near as rosy for Mourinho, who must weigh his priorities ahead of Thursday's return leg against Anderlecht.
David de Gea is expected to return in goal, having missed United's last two games with a hip problem.
But Phil Jones (foot) and Chris Smalling (knee) remain out and Juan Mata has been ruled out for the rest of the season with a groin injury.
United are four points off the Champions League berths and have a game in hand on fourth-place Manchester City.
Winning the Europa League still looks their best chance of Champions League qualification, but Mourinho says they will not abandon the battle for a top-four finish.
"If we arrive into a situation in the Premier League - I hope not - where mathematically the top four is not possible, then the easy decision is to rest them and go with them in the Europa League if we're still in the competition," he said.
"But at this moment we are in a position where we have two matches in hand.
"If we win both matches, we are in the top four. We have to fight for every game."
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