Their squad is crammed full of wonderfully potent performers such as Juan Mata, Paul Pogba, Romelu Lukaku and Alexis Sanchez, yet the Premier League table, which shows them 16 points behind City, does not lie.
The fact that it handed the title to United's arch-rivals City, a week after they had beaten them, means it will reverberate around the football world.
Jay Rodriguez headed in a 73rd-minute winning goal to seal only a second win since August and allow City to clinch the title without kicking a ball.
United pushed numbers forward in the closing stages, but Foster never really looked in danger of being tested again as United succumbed to a defeat that was celebrated by the blue half of Manchester with even more vigour than usual.
The West Brom win wasn't without controversy.
Few minutes later McClean nearly doubled West Brom's lead but his low shot went just wide of the target. There was no late dramatic theatre on this occasion as nothing would come off for the subdued Reds and the Baggies held on for an unexpected first league win since January.
"Manchester City, we won it for you, " chanted the West Brom fans at the end of a match greeted by jeers by United supporters.
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But you wouldn't have guessed it with the way Mourinho set his side out on Sunday afternoon, at Old Trafford no less.
The dynasty will only be built on European success, though, and after the quarter-final exit to Liverpool, City's owners, who want a gilded continental powerhouse to match United's global lustre, will demand it and back those demands with huge funding.
Despite the win, West Brom remain bottom on 24 points with four games left to play.
This sort of unfavourable comparison explains why Thierry Henry questioned Pogba following the West Brom defeat: 'As soon as the game started, something was weird. It looked like Lukaku's powered header from Nemanja Matic's cross was destined for a goal until Foster did a more than passable impression of De Gea with a reflex stop to keep his goal intact.
"The last Premier League was not 20 years ago, it was three years ago".
United should have been surfing the crest of the wave following that victory, but instead they fell flat against West Brom.
Nobody expected this result, so it was a nice surprise for City to become champions one week earlier than they had anticipated, and for that they owe thanks to West Brom, who made sure they knew that.