However, United were shocked 1-0 by bottom club West Brom at Old Trafford, to hand the title to their neighbours.
City manager Pep Guardiola might have rubbed his eyes in disbelief at events at Old Trafford when he returned from his round of golf with his son.
"You look at the signings Mourinho has made".
Mourinho's side had dominated possession but created few clear chances and their loss leaves City 16 points clear with just five games remaining. However, their showing has relatively no positives with Paul Pogba and Alexis Sanchez struggling to replicate their recent performance.
It wasn't the best day for Romelu Lukaku against his former club, either.
The first half was a bad advert for the English top-flight.
"Manchester City won the title because they won more points than everybody else, because yesterday they won against Tottenham, because during the season they lost only two matches". Everything was slow. Everyone was one more touch, one more trick, one more flick, one more turn.More news: 7 inmates dead and 17 injured after SC prison fight
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And that was also the case on Sunday, as United failed to spark the imagination in any tangible way even though they were playing a side that had hadn't won in the league since January. Reportedly, United have scouted Tierney multiple times this season, and they intend to finalize the deal this summer. "We wanted to dribble and dribble, and everything was complicated".
The irony that this is exactly how Manchester City play will not be lost on anyone.
The United manager remains confident in his own ability but said his side must replicate City's consistency next season. Vincent Kompany did, with images showing the City captain celebrating at his in-laws' house where he was having dinner.
"I trust in my work, that's for sure", said Mourinho. I think with my experience you don't win titles with inconsistency.
They have equaled the record for quickest title success held by United's 2000-01 team, winning the league with five games remaining.
City could yet finish the season with the most points, goals and wins from a single Premier League campaign.
The form has been good in 2018 and the team already have more points than in any season post 2013, but we all know that's not how United will be judged.