Chelsea are three points behind Premier League leaders United with three games left and can go top with a victory.
"It's like a final for us. We wanted to play in the final of the Champions League but we have to be happy to play this kind of final. This is a different final but for us we can compare this game to a final," Ancelotti told a news conference.
Chelsea were the last side to win at United over a year ago but lost to Sir Alex Ferguson's side last month in the Champions League quarter-finals when they went out 3-1 on aggregate.
Ancelotti said he was trying to keep everyone calm ahead of the big game to conserve their energy for the task ahead.
"We have to prepare this game like a final. To prepare a final you have to stay relaxed as much as possible," the Italian added at the club's training ground.
"There is a lot of pressure around you to prepare this game and you have to have the skills to stay relaxed, to maintain a good control of your emotions, don't be too afraid, too worried because to be too worried you lose energy before the game and you have to use all the energy during the game."
United have 73 points to Chelsea's 70, with both on the same goal difference, meaning the London side will lead the standings if they win while a victory for United would leave Ferguson's team needing just one more point to clinch their 19th title.
