Brighton boss Chris Hughton believed the linesman got a key decision wrong in the narrow defeat by Manchester United.
Well-drilled Brighton threatened to cause an upset as they impressed on their first trip to Old Trafford since 1993 but United ground out the result.
Jose Mourinho even claimed Brighton deserved more than they got while Hughton was left frustrated as he felt United should not have been awarded the corner which led to their winner when Solly March and Romelu Lukaku battled for the ball.
Hughton said: "My view at the time was that it wasn't a corner. When the linesman gave it I presumed he must've seen something but looking again, it wasn't a corner.
"What touched him was Lukaku's foot. I hope I haven't got it wrong but when you see it again it's not a corner. But we did have an opportunity to clear the ball before that and there is still a bit to happen after that.
"Even after that we tried to get back in the game. It wasn't to be in the end."
Brighton were unlucky to see their five-match unbeaten run come to an end after an assured display where they panicked the hosts with some dangerous crosses.
"We didn't deserve to lose," Hughton said.
"It was one of those games where it was going to take a bit of brilliance or a bit of fortune - they got the fortune with the deflected goal. Some of our play was good and restricted them to minimal chances. Apart from one save from Matthew Ryan I can't think of a clear opportunity in the 90 minutes."