In his post-match press conference, Mourinho made reference to the eight titles he has won in his managerial career and why this was a reason behind why he did not "feel super happy" when his side defeated City last weekend.
The Red Devils were aware that if they beat the Baggies on Sunday, they would once again have delayed the Citizens' title celebrations for one more week, but this was not to be as Jay Rodriguez popped up with a 73rd-minute header to clinch the game for the relegation strugglers.
"You see the difference of attitude of some players today compared with other weeks; relax, too stylish, one more touch, one more turn, one more flick".
This frank assessment from the Portuguese manager tells you everything you need to know about United's performance - a laboured, lacklustre loss of both the match and the title.
After a mixed first season in England, Guardiola faced questions about whether his methods were a good fit for the Premier League.
City had moved within touching distance of the title with a 3-1 win at Tottenham on Saturday.
"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. Eight titles are eight titles and three Premier Leagues are three Premier Leagues.
United have scored a full 30 goals fewer than City this season and Mourinho has not managed to get his side to click, despite being able to bring on further talent such as Marcus Rashford, Jesse Lingard and Anthony Martial.
"The mental level, the day by day, everything must be consistent until the last day so one of the things we have to improve is consistency", he said.
Manchester United went down 1 - 0 to West Brom, a result so unexpected, City coach Pep Guardiola went to play golf instead of watching. "I knew that sooner or later that would happen". They lost only two matches, that is why they were champions. I win titles. My last Premier League title was not 20 years ago, it was three years ago.
This is how Manchester #United lose the #Premier League title race, not with a fight but with a whimper.
Guardiola failed to win a trophy during his first season in English football but has now added the Premier League to the EFL Cup crown collected against Arsenal in February.