"Premier League Champions 17/18", City tweeted soon after the final whistle, when the fifth English top-flight title of its history was assured. Chris Smalling had an attempt as the clock wound down and the full-time whistle saw City crowned champions.
The Citizens only needed one more win to secure the title following their win over Tottenham Hotspur, but the Red Devils' loss to West Brom means they have now mathematically secured the title.
In his pre-match press conference on Friday, Mourinho told a journalist that he only needs four points to stay second and the derby win against Manchester City last week should set their hopes on course.
Over £12m was traded on the 2017/18 Premier League Winner market, but with City effectively running away with the title - eventually winning it with five games remaining - no team other then the winners traded at odds-on, or even notably shorter than their pre-season odds.
It's the third Premier League success for the club following the titles won in 2012 under Roberto Mancini and 2014 under Manuel Pellegrini with captain Vincent Kompany, David Silva, Sergio Aguero and Yaya Toure involved in all of them.
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The Baggies have scored just 26 Premier League goals in 2017-18, the same total Manchester United have registered in the first half in games alone.
The English goalkeeper, who recently turned 35, averaged 2.19 saves per game before the match against his former club and pulled off another hat-trick of saves to deny United on Sunday.
United were second-best all afternoon and Darren Moore's men earned their reward for a spirited display thanks to Jay Rodriguez's close-range header 17 minutes from time.
That could see Juan Mata recalled while Marcus Rashford may get the nod ahead of Anthony Martial amid rumours both players are becoming unsettled due to a lack of regular starts.