MANCHESTER -- Jose Mourinho has congratulated Manchester City on their Premier League title triumph before complaining that his players made Sunday's shock loss to West Brom too "complicated."

City were crowned champions with five games to spare after United lost 1-0 to bottom side West Bromwich Albion at Old Trafford.

Mourinho says they are deserved winners but the 55-year-old insists he is the right man to bring the trophy back to Old Trafford for the first time since 2013.

"I don't know if I was the first or the second or the third, but I congratulate them face to face when I had the chance to do it," the Portuguese coach told a news conference.

"I know that sooner or later that would be and if I was in that position I would be very upset if somebody say they won the title because Manchester United lost to West Brom. They won the title because they were the best team."

"I trust in my work, that is for sure. I have no reason to not trust because eight titles and three Premier Leagues are three Premier Leagues, and the last was not 20 years ago.

Manchester United's loss to West Brom handed Manchester City the Premier League title on Sunday. Getty

"It was three years ago and I know how to win. I believe in myself but I don't play."

United followed up their dramatic 3-2 win at the Etihad Stadium with a shock defeat to West Brom, who had only won three games all season before kick off.

And Mourinho said the past seven days have highlighted what needs to change if they are to win the league next season.

He added: "Not just the performance level but the mental level, day by day, everything must be consistent, since day one until the last day so one of the things we have to improve is consistency."

West Brom had Ben Foster to thank for two fine saves from Romelu Lukaku either side of half-time before Jay Rodriguez scored the winner 18 minutes from time.

Mourinho substituted Paul Pogba before the hour mark and threw on Marcus Rashford and Anthony Martial as he went in search of a goal.

After the final whistle, the United manager criticised his players.

"We were masters in complicated football," he said.

"Everything was complicated, we couldn't play fast or think fast, everything was complicated, one more touch to control, one more turn, one more flick, one more trick and we always gave them the opportunity to be solid.

"When we have the ball, we want to run with the ball, we want to dribble, and everything was complicated and probably in our best period where we were moving the ball better and the team was thinking faster and the team had more width was when they scored."