Sir Alex Ferguson accused David Luiz of getting Rafael da Silva sent off and claimed Chelsea's players put pressure on referee Howard Webb throughout their 1-0 win at Old Trafford.
Rafael was red-carded in the 89th minute for kicking out at Luiz but Ferguson insisted the Chelsea player elbowed the United right-back twice beforehand and was guilty of play-acting to get his compatriot dismissed.
He said: "He [Rafael] was elbowed. He retaliated. That always happens, the player that retaliates gets the heavier penalty. It was quite clear Luiz has elbowed him twice. The referee has been bought by the fact Luiz has rolled about.
"The referee hasn't even seen it at all. He has gone with the fact Luiz has rolled around on the floor and that has convinced him it is a red card. You see that a lot with European, foreign players and South Americans.
"Certainly the refereeing decisions went against us. They surrounded the referee all day, four or five players all the time. I think that affected the referee."
Ferguson branded Chelsea's winner, an 87th-minute Juan Mata shot that took a deflection off Phil Jones, "lucky" but did not complain that United should have had a free-kick for a challenge by Ramires on substitute Wayne Rooney seconds earlier.
He added: "I don't think Wayne was fouled. But the referee was giving us nothing anyway. We didn't expect anything."
However, he had no complaints about the result. "Chelsea deserved the win," he added. "I can't make any excuses for our players in terms of performance. The final big effort was last week against Arsenal. Today, the edge to the game was off."
Rafa Benitez challenged his players to secure their place in next season's Champions League by defeating Tottenham on Wednesday after earning a "massive" win at Old Trafford.
Their goal difference is 16 goals better and Benitez hopes to seal a top-four finish at Stamford Bridge.
He said: "It is massive for us, because we knew we needed to get six or seven points and hopefully we can stay there until the end. It was an important step forward.
"This game was difficult but Wednesday will be even more important. Still it's crucial because winning we will be there but it's even more important to them so it should be a great atmosphere at Stamford Bridge. We will go and try to win because we know we can guarantee the top four [finish].
"The goal difference is too big so if we win we can be there but Tottenham are a good team so it's a big game for both. We are in the driving seat, hopefully we can stay there until the end."
Benitez is waiting to see if Eden Hazard will be fit to face Tottenham after the Belgian missed the victory at Old Trafford.
"He had a little problem in his calf," the interim manager added. "He could be available [for Spurs] but it's not easy. He is working with the physios so we will see."
The Spaniard hailed his compatriot Mata after the former Valencia player made another vital contribution.
"He could be player of the year for everything he did for us," he added. "He is a very influential player in the game. Juan Mata is a great player and has the intelligence and ability to change the game."