They've acquired the natural goalscorer they had so longed craved in Romelu Lukaku and have forged the perfect balance between integrating the youthful exuberance of Marcus Rashford and the experience of Marouane Fellaini.
But, perhaps most tellingly, Mourinho seems to have reinvigorated a number of first-team squad members who may yet prove pivotal to their ambitions this season.
None more so than Phil Jones.
The England international has battled chronic injury woes in the last few years to cement his place in the heart of the United back four. And he has done so with aplomb.
Alongside Eric Bailly, the dynamic duo have been invaluable in helping Mourinho's men secure five clean sheets in their first six Premier League matches.
Jones, who appeared to have lost his way at Old Trafford, has fought his way back up the pecking order and has played an instrumental role in United's early season success.
Saturday's uninspiring 1-0 victory over Southampton at St.Mary's was indebted to stoic defending as the red half of Manchester maintained pace with neighbours City at the top of the Premier League table.
Mourinho seems to have found the perfect balance in a back four that, although rattled at times by Saints' second-half rally, held firm to guide United to a second away victory of the new season.
And while the Old Trafford club's quest for Premier League glory will be heavily influenced by the goalscoring instincts of Lukaku, keeping Jones fit could prove just as vital at the other end.
The 25-year-old's stubbornness and determination seems to be rubbing off on his defensive colleagues, who this season seem better equipped to mount a sustained title charge.
Southampton were relentless in their pursuit of an equaliser but marshalled by Jones and Bailly, United were unshakeable defensively and constantly thwarted the Saints.
Mourinho lauded United's resilience following Saturday's triumph, pointing to the leadership skills of Jones, Bailly and Chris Smalling as keys to victory on the south coast.
“They were very good,” Mourinho marvelled.
“We did for 20 minutes what the majority of Premier League teams are doing this season, which is to play defensive with five at the back.
“We had chances to kill the game. We had chances to score the second goal but then, honestly, I felt Southampton coming on strong. I felt their manager enthused and excited.
“I then made the decision to bring on Smalling and the team was very solid, good organisation, good spirit and it's an amazing three points.”
Celebrations at full time were rather muted given United were forced to work excessively hard by a resilient Saints side.
Jones, in particular, looked out on his feet and his impressive start to the season has earned him rave reviews throughout the league.
Interestingly enough, the England centre-half has already featured in a third of the Premier League games he did last season, making just 18 league appearances in Mourinho's debut campaign.
Now, however, it would appear that the Portuguese master tactician has entrusted the former Blackburn youngster to marshall United to a first title in five seasons.
“I think they were really tired,” Mourinho reflected.
“I saw some players not sharp. Great spirit, always trying but not the same sharpness.
“So when your opponent is coming with everything at you, we had to do it (play three centre halves) for 10-15 minutes and we were solid.
“This is nothing. this is just a start.
“This time last season we would have had five or six points less so we are better this season.
“The difficult period and accumulation of matches hasn't arrived yet. This is just the beginning.
“In October all of that comes. It's going to be difficult, I really think six teams are going to fight for the title.”