Alex Ferguson condemned David Luiz as lacking professionalism and accused the Brazilian of "rolling about like a dying swan" after he was pictured smiling on the ground following Rafael da Silva's dismissal for a foul on the Chelsea defender.
Luiz, who was also accused by Ferguson of elbowing Rafael prior to the foul which led to the Manchester United defender being sent off by referee Howard Webb, fell to the ground at the feet of assistant referee Sian Massey following a retaliatory kick by Rafael.
Television footage then showed Luiz putting his hands to his face before appearing to grin as Webb approached Rafael to issue the red card.
The incident sparked a fiery end to a game which was won by Juan Mata's 86th-minute strike, courtesy of a heavy deflection off United defender Phil Jones, and United manager Ferguson insisted that Rafael's dismissal – the third of his United career – was a down to Luiz's behaviour.
"The ref has been bought by the fact Luiz is rolling about, but whether the ref will doing anything about it, I doubt it very much," Ferguson said.
"Rafael was elbowed and he retaliated. The player that retaliates gets the heavier penalty, but it was quite clear Luiz has elbowed him twice.
"He (Rafael) retaliates but Luiz quite clearly elbows him twice then rolls about like a dying swan and that convinces the referee.
"He was smiling, it's bad. What kind of professional is that?"
When asked about the sending-off and Luiz's reaction, Chelsea interim manager Rafael Benitez claimed not to have seen the incident.
"I didn't see the incident or replays," Benitez said. "I haven't seen it and I will not say too much – there are 200 incidents each weekend in the league."
Rafael will now serve a three-match suspension for the straight red.
"I wouldn't say it was violent conduct," Ferguson said. "The referee has gone with the fact Luiz has rolled around on the floor – you see that with these European, foreign and South American players, and that has convinced him it is a red card.
"It was rash what Rafael did. He is a young lad, he should know better, but retaliation never works."
Chelsea's victory could prove crucial in the three-way battle for Champions League qualification against Arsenal and Tottenham. With Spurs due at Stamford Bridge on Wednesday, Chelsea can all but secure qualification with another win and Benitez admitted that the three points at Old Trafford were hugely important.
"Its massive for us, because we knew we needed to get six or seven points to guarantee the top four," Benitez said. "Hopefully we can stay there until the end and this was an important step forward. For us, every game is massive now.
"We did really well, but we now have to beat Tottenham and that will not be easy. The goal difference is big (in our favour) so if we win, we can be there. But Tottenham is a good team."
Benitez, who revealed that Eden Hazard missed this game because of a calf injury, proved evasive when asked about speculation linking the former Liverpool manager with a move to the Bundesliga with Schalke 04.
"The main thing for me is to concentration on the next game so I will try to do that," Benitez said.
Having suffered their third home league defeat of the season, United's prospects of eclipsing their Premier League record winning margin of 18 points have been diminished.
And Ferguson conceded that his players, who will receive the Premier League trophy following next Sunday's game against Swansea, lacked the intensity required to beat Chelsea.
"There is always an expectation that we should do better and we expected a better performance," Ferguson said. "It was difficult for players coming in. Chelsea had everything to play for and some of our players haven't played for quite a while. That being said, we should be doing better.
"There was no edge to the game, I think Chelsea were the better team. It's been a long season (for United) and the final effort was last week against Arsenal. The edge was off and we took our foot off the pedal. We didn't play well enough." (© Daily Telegraph, London)