Wigan boss Roberto Martinez has accused Manchester United striker Danny Welbeck of diving and claimed that he should have been sent off at Old Trafford.
The initial incident happened in the first couple of minutes during United's 4-0 win, when Welbeck went down under Ali Al Habsi's challenge. It seemed innocuous at the time, and TV replays showed there had been no contact as Welbeck went to ground.
Javier Hernandez missed the penalty but later in a feisty contest, Welbeck lunged in on Franco di Santo, which Martinez felt warranted a red card. And the Wigan boss said: "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."
He added: "I am not arguing whether they should be in the game or not. That is for others. But with the laws as they are, you cannot tackle people like that.
"The foot is over the ball. It is reckless and dangerous. It is a red card, for a Wigan player, Manchester United, everyone."
Despite that, Martinez did not blame referee Michael Oliver for his side's defeat, but the Latics chief admitted he was irritated at that first spot-kick call, which he felt set the tone for the entire afternoon.
"I was (irritated)," he said. "You could see it. You know what he is trying to do.
"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. Today the penalty is as bad a decision as you are going to see in the Premier League."
United's biggest win of the season was scarred by a short burst of anti-Liverpool chanting from a small minority of home fans. On Friday, Sir Alex Ferguson expressed the hope that, following this week's damning judgement on the Hillsborough tragedy in 1989, when 96 people died, a line could be drawn in the sand on the sour relations between the two sets of supporters.
It is a feeling shared by all senior figures at Old Trafford, who hope that the songs are not repeated when United head to Anfield on Sunday, and United said: "The manager has made the club's position very clear on this matter. It is now up to the fans to respect that."