By Julien Pretot

PARIS (Reuters) - Having watched Roger Federer raise his game to new heights on clay in his epic semi-final, five-times champion Rafa Nadal is not sure his brilliant best will be enough to win the French Open final on Sunday.

World number one Nadal, who considers Federer the greatest player of all time, also hit his stride on the Paris red clay in a straight-sets win over Andy Murray on Friday.

However, Swiss third seed Federer was truly impressive as he snapped Novak Djokovic's 41-match unbeaten run in 2011 in one of the greatest matches played at Roland Garros.

"I will have to play at my best and sometimes it's not enough to win," Nadal told a news conference on Saturday. "He is the best player in history."

The soft-spoken Spaniard does not even take comfort in his three previous victories against Federer in the French Open final.

"When you play against him, you can win but you have a lot of chances to lose. I will try to play my best and we will see," the 25-year-old Nadal said.

The left-handed Nadal, who beat Federer in the 2006, 2007 and 2008 Roland Garros finals, will take nothing for granted on Court Philippe Chatrier.

For a start, he is not surprised to be facing the Swiss, who has not played a grand slam final since the 2010 Australian Open, instead of Serbian Djokovic.

"It's not a surprise. You're more surprised than I am. We know how good is Roger," he said. "It is not a surprise to see Roger in another grand slam final."

He dismissed the fact that Federer managed only four games in their last French Open final.

"He has more confidence; he knows he is playing fantastic. But after yesterday's victory, he must feel very confident," said Nadal. "(Our last French Open final) was three years ago. It's impossible to compare."

"Well, honestly, I feel very well," he told reporters on Friday.

"I think I move very well. I'm never stressed. If there is a ball that you miss, it's just because the other one played it very well, and not because I made a mistake or I played bad tennis on the return, on my serve. That's why I'm very happy at the moment with my game."

(Editing by Clare Fallon)