Referee Michael Oliver booked Herrera for diving and left Mourinho with a distraction after his side were outplayed at Old Trafford.

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"Clear penalty. I am sorry for us and sorry for Michael, I think he had a good performance but it was a clear penalty," the Portuguese said on Sky Sports.

"The referee made a mistake, which can happen. Last season we had a similar situation here against Man City. We were winning 2-1 and Mr Clattenburg didn't see the penalty - (Claudio) Bravo on (Wayne) Rooney - and this one also.

"I am sorry for Michael Oliver because he had a good performance. The referee had a good match but he made one mistake and his mistake was crucial to the outcome of the match."

With United's deficit now into double figures, City are clear favourites to lift the Premier League title in May.

Mourinho says his side will continue to fight.

He added: "They are a very good team. I think they are lucky, they had all the decisions in their favour but Tuesday is another day in the Premier League and I am pretty sure all of us, us in second, Chelsea in third, and fourth and fifth and sixth, everyone is going to try to fight for points and try and reduce the distance.

"Of course, their advantage is a very good one."

Pep Guardiola swatted away Mourinho's suggestions and was left purring at his side's performance.

"Last season it was the same, we won here and the comments were the referee," the City boss said.

"And today we have won and the comments are the same as well. We are an honest team. We want to play and we did it. We came here to play.

"Wow, we played outstanding. To play here at Old Trafford and play the way we played with the ball and trying to be patient, it was so, so clever.

"We are so happy because it was an important game for us and at our rivals, so big credit to the players.

"I am happy and this style of play we can do it in England. People have said the way we tried to play at Barcelona is not possible in England, but it is always possible to play football, keep the ball and we did it.

"I always believed that we can do that, anybody can play the way they want and that is why football is beautiful. I am happy to go to places like Stamford Bridge and Old Trafford and against contenders, we have beaten them."

Guardiola is not letting his side believe they have the title wrapped up but knows they are in a good position.

"It means a lot in terms of the way we played for our confidence, but in three days we go to Swansea.

"Eleven points plus goal difference - it is 12 points - and we have more points than Chelsea, Liverpool and Arsenal this week.

"In December it is impossible to be champions but that gap is very good for us."