Ancelotti knows the role of referee Howard Webb will be crucial when his side go in search of a victory at Old Trafford on Sunday that would put them in pole position to retain the Premier League title.

Ferguson believes Chelsea have benefitted from mistakes by the officials in their last three league meetings with the Blues and he was handed a five-match touchline ban after launching an astonishing attack on referee Martin Atkinson following United's 2-1 defeat at Stamford Bridge in March.

The Scot has never been shy about criticising officials and often uses his press conferences to call for strong refereeing before big games.

But Ancelotti believes that kind of behaviour presents a bad image of the sport and he is adamant managers gain nothing from taking out their frustrations on the officials.

"You don't get an advantage to speak against the referee. The decision is already taken," Ancelotti said.

"Also for the image of football you have a social responsibility. For the young kids who look at you as an idol, the image on and off the pitch is important.

"Sometimes when things are not good you can speak about things that go against you.

"But I don't want to put pressure on the referee. Howard Webb is a fantastic referee, he has the skills to handle the occasion.

"If the referee has no experience maybe you can be a little worried about this but with Webb there is no problem.

"I have trust in the referees in England. They make mistakes but this is normal, you have to accept that or you have to say there is a conspiracy and I don't believe that."

The stakes could not be higher on Sunday as a win means Chelsea will go top, ahead of United on goal difference, with just two games to go, while a victory for Ferguson's team will leave them needing only one point to clinch a record 19th league title.

Ancelotti believes his team have a psychological advantage over United as they have nothing to lose, while the leaders would be shattered to surrender top spot after holding a 15-point lead over Chelsea at one stage.

"Mentally we can have an advantage because I think Man United hoped that they wouldn't have to play this kind of game against us," Ancelotti said.

"If they had more of an advantage they could have a different game, an easier one maybe. Now they have to fight again for the title, maybe two or three weeks ago they didn't think they would have to fight so much.

"They had a fantastic record at home this season and they drew just one game but now it is time for us to win."

If Chelsea do lose on Sunday, there will inevitably be renewed speculation that Ancelotti will be sacked after a barren season.

Even so, Ancelotti doesn't believe the result of Sunday's game will decide his future.

"I don't think so, no," he said. "The behaviour of the club is the same, nothing changed with a victory or defeat, they maintained a very good support for me.

"I am calm. If they decide to change there is no problem. It is not crazy to think they could change because every club has the possibility to do this at the end of the season.

"I tried to do my best. They have to check my job. If they think it is good, I will stay."