United manager Jose Mourinho had long given up hope of winning the title, instead focusing on finishing second.
Pep Guardiola's side are now uncatchable at the top of the table after United's shock defeat to the bottom-of-the-table Baggies after Jay Rodriguez's 73rd-minute strike sealed their fate.
But, just a week after spoiling City's title party by beating their local rivals 3-2 at the Etihad, the way United abjectly gifted the title to their neighbours will sting.
"Everything is to play for as I've said all along, we're in a relegation battle until we're safe".
Given the way they have demolished all challengers in the league, it was apparent months ago that it was only a matter of when rather than if City would take the title.
"I don't think we deserved to lose but we gave them the opportunity to win the match by being solid in defence and smelling a chance in a set-play which they did".
"That doesn't make me feel super happy and in my opinion affected for sure some of the people that was too happy". Paul Pogba was his usual frustrating self whilst United reverted back to their usual sterile brand of football which fans have been subjected to so often at Old Trafford this season.
"Given how easily they won the Premier League title this season, it is no surprise that Manchester City have opened up as the odds-on favourites to do it all over again in the 2018/19 campaign", said Coral's John Hill. Interestingly West Brom have won 3 of their last 5 games against United at Old Trafford.
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After the match, Mourinho made it clear he was unimpressed with his players' efforts, lack of fluidity and desire.
"I trust in my work", he said.
United hold the current record Premier League winning margin of 18 points and that could also fall to City.
Mourinho isn't known for mincing his words. You do not win titles with inconsistency.
"Everything must be consistent until the last day".
"One team was dominant in Germany and one had (Lionel) Messi, but we are nothing without the team".
The first half was a bad advert for the English top-flight.
Jake Livermore forced a smart save out of David De Gea on 12 minutes with a left-footed shot from 12 yards out after being played in on the right by Salomon Rondon, who steered a header well over the target from James McClean's cross on the left moments later. Nemanja Matic panicked at the delivery and headed back inside to Rodriguez, who could not miss from three yards out. We didn't create enough chances to score and West Brom were fighting for survival. It is nearly certainly too little too late for West Brom, who look doomed to relegation. "I want to bring a family atmosphere to the club".