Wigan boss Roberto Martinez accused referees of favouring Manchester United at Old Trafford after saying Danny Welbeck should have been sent off.
Martinez was infuriated when Welbeck was awarded a soft penalty in the opening stages and believes the United striker should have seen red for a reckless challenge on Franco Di Santo towards the end of the game.
TV replays showed no contact when Welbeck went down under a challenge from Ali Al Habsi but referee Michael Oliver pointed to the spot.
Javier Hernandez saw his penalty saved by Al Habsi, but Martinez was still unhappy with decisions which went against his side in the 4-0 defeat.
"I have come to United three times before today and for whatever reason we don't seem to be measured in the same manner as the team at home," said Martinez.
"Today the penalty is as bad a decision as you are going to see in the Premier League. In many ways, you feel as though you are fighting against a mountain.
"There were tackles flying around that if they had been the other way round there would have been a couple of red cards.
"For Danny Welbeck's last challenge, his foot was over the ball on Franco. It is completely reckless. Under the new regulations you cannot do that. It is a red card, for a Wigan player, Manchester United, everyone."