Jay Rodriguez headed home to secure rock-bottom West Brom a win at Old Trafford that was as remarkable as it had looked unlikely.
Manchester City have already won more points from their 33 league games this season (87) than 11 of the previous Premier League champions had won at the end of their title-winning campaign - this includes their last title win in 2013-14 (86).
A serial victor as a manager with Barcelona and Barcelona, Guardiola ended his first year in England at City without silverware - his only failure to win a trophy since his managerial career started back in 2007.
Manchester United fans were far from pleased with Paul Pogba's poor performance vs West Brom on the back of his incredible display vs Manchester City.
"As much as this has been a record breaking season, this one's for you, the fans, this is why we do it!" said the skipper.
Pogba was singled out by Mourinho and not for the first time this season the Frecnhamn finds himself under fire at Old Trafford.
Manchester United manager Jose Mourinhosaid: I think we were deservedly punished.
"I trust in my work, that is for sure", added Mourinho.
This shouldn't shadow what has been a fantastic season for City, with many fantastic wins helping them on their way to the title.
Mourinho revealed he suspected his side would be beaten by West Brom when he noticed his players losing their focus after the derby win.
"It's incredible the way we played and I am so glad to be here and be part of this club", he said on the club's website.
Mourinho is quoted as saying by Metro: "I told Paul after the City game I don't expect him to be man of the match every week".
The 2012 title win had the infamous last-gasp goal by Sergio Aguero. But I expect you to be consistent in a certain level.
WE SHOULD HAVE HAD A PENALTY IN THE FIRST HALF "Paul Tierney [the referee] was unlucky in one decision [the challenge by Craig Dawson on Ander Herrera] but I don't blame him at all - it's football". But I saw lots of people in the moon because we won against Manchester City like winning against Manchester City was the most important thing of the season.