The lose for United means that City team can not be displace from the top of the table, thereby given Pep Guardiola his first Premier League title in his second years as that Manager of Manchester United team.
Jose Mourinho's side had prevented its neighbour winning the title with a stirring comeback last weekend, but an unlikely defeat to the Baggies secured a third Premier League title for its cross-city rival.
United had to at least draw to keep the title race mathematically alive, but they were stunned at Old Trafford when Jay Rodriguez headed home after the break.
In a less than fanfare Sunday afternoon in Manchester, it was the faltering of the Red side of the city which saw Manchester's blue affirmed as League Champions.
"We did not deserve to lose, we gave them opportunity to win the match".
A week after City surrendered a 2-0 lead to lose 2-3 to United and squander the chance to wrap up the title in flawless style against their arch-rivals, it was relegation-bound West Brom who served it up on a plate.
City need just nine points from their final games to set a new record for most Premier League points, while another 11 goals would see them set a new goal-scoring record.
The defeat at Old Trafford helped the Etihad outfit mathematically win the Premier League. After completing a year-long sabbatical, he returned to action by managing Bayern Munich where he won the Bundesliga League Title three times. I'm sorry, it's much more important what these guys have done this season.
As for City, it has a month to finish a season with the most points, goals and wins in a single Premier League campaign.
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"Not the defeat, I think it's too heavy, but not to win this match".
"That doesn't make me feel super happy and in my opinion affected for sure some of the people that was too happy".
"They lost only two matches because they were the best team".
The irony that this is exactly how Manchester City play will not be lost on anyone.
At the age of 30, Jonny Evans already has ample experience of playing in the Premier League, unlike Aymeric Laporte.
Although Mourinho says that he is not expecting Pobga to perform like that every week, he does want the midfielder to be more consistent for his team moving forward.
Mourinho's side had dominated possession but created few clear chances and their loss leaves City 16 points clear with just five games remaining.
"After beating Manchester City we wanted a winning spirit until the end of the season but today was one of those days".