The sides meet for the fifth time this season and for the fourth in just over two months for a match which could ultimately decide the destiny of the championship.

Never before have the two clubs gone head to head so often during a single campaign, with the pair contesting the Community Shield and Champions League as well as the Premier League.

Such familiarity can often breed contempt - as Barcelona and Real Madrid found out.

But Ancelotti feels Chelsea and United's problems on Sunday will be more straightforward than that, especially as his only real selection dilemma appears to be whether or not to start with Fernando Torres.

"I think that Chelsea and Manchester United don't have secrets," he said.

"They know very well every aspect of their football and their skills. They know us, we know them.

"I learned that (Wayne) Rooney is the key player for United, and also (Ryan) Giggs against us was the best player."

Such familiarity may play into the hands of United, who do not need to win the game to retain their stranglehold on the destiny of the title.

Despite the sensational late-season surge that has seen Chelsea close to within three points from 15 adrift in a little over two months, only victory will do for the visitors.

Ancelotti's side had looked like running away with the title back in October but their worst run in the league for almost 15 years could still end up costing them dear.

Ancelotti conceded: "If I have to think about our season, it was not so good.

"Our bad moment was too long, I think. We could do better there. But now, destiny has helped us to fight for the title again."

Providence too, judging by last weekend's results, which saw Chelsea beat Tottenham 2-1 with two goals that never should have stood and United lose 1-0 at Arsenal.

Ancelotti said: "If Arsenal didn't win that game, it would be a different atmosphere around our game.

"The turning point was Arsenal and our victory against Tottenham."

That might have been the moment the title race was blown wide open but it was certainly not the turning point in Chelsea's season.

That arguably came after last month's Champions League defeat against United, when the Blues fought back from a goal down to win at West Brom.

They have not looked back since, taking maximum points from the next three games.

Ancelotti said: "Against West Bromwich it was a good game because it was after the defeat to United.

"It was a turning point because we were able to close the gap and get the three points, to give interest to the game against United. Six points behind and this match wouldn't be so interesting."

Chelsea won the corresponding fixture late last season, a victory which ultimately saw them win the title.

Ancelotti said: "Obviously, I want to remind my players of that, as I think (Sir Alex) Ferguson will remind his players the game they played against us in the Champions League.

"We needed to win there last year and we won. I hope this year will be the same."

United are unbeaten at Old Trafford since that day and have dropped just two points there this season.

"It's time to win," said Ancelotti, who will give his players the same team talk he used last season.

"It's always the same message to prepare for this game. Be calm, relax, and believe in yourselves.

"There is not a lot else to do. The players are motivated themselves.

"The problem is the fear. Being afraid - to lose energy being too afraid."