A frustrated Chris Hughton felt his Brighton & Hove Albion side deserved a point at Old Trafford and criticised the linesman for giving a corner that never was in the build up to Manchester United's goal.
Ashley Young's 66th-minute effort took a huge deflection off Lewis Dunk as the defender attempted a trademark block and ended up in the top corner for the only goal of the game.
And Albion were left to rue the goal coming from a corner which they felt should not have been with the ball taking a touch off Romelu Lukaku, but their protests were ignored as United extended their winning run to eight Premier League games at Old Trafford.
The Seagulls defended superbly throughout and had a number of decent openings of their own at the other end, but their impressive performance went unrewarded as their five-game unbeaten run was ended.
Hughton said: "I am frustrated for a couple of reasons. One, we had an opportunity before the goal to clear it and two, I don't think it was a corner. Of course the manner of the goal is very disappointing.
"Just to be clear, I went on one of the stations and said it wasn't a corner, but somebody told me Solly (March) has said he had touched it. Well no he didn't, what (he said) touched him was Lukaku's foot.
"I hope I have not got it wrong, but when you see it again, it is not a corner. Although we did have an opportunity to clear the ball before that and a bit that went on after that. It was a fortuatus goal for us to give away, but even after that we tried to get back into the game and it wasn't to be in the end.
"From where I was it looked like it wasn't a corner, but I presumed the fact that the official was that close that he must have got it right. He is the only one with the view he has got and a better one than the referee has, you expect him to get it right."
Post-match Jose Mourinho heaped praise on Albion saying the were the team that has caused them most problems this season.
Hughton added: "It's always nice to hear that from opposition managers, but we are incredabily disappointed because I felt we deserved to get more from the day. Particularly because when you talk about chances, we didn't create too many, but got into some really good positions, but over the 90 minutes Maty Ryan has only had to make one very good save.
"Apart from that I can't think of one clear chance they have created. Certainly as an away team I felt we were value for a point.
"I thought Lewis Dunk was very good and even at 1-0 down when he has gone forward if he has a little bit more compsure at the other end, it might have been another story, but he was very good today."