LONDON (Reuters) - Roger Federer said on Saturday his Wimbledon final opponent Rafael Nadal had made him a tougher player because of their great rivalry.

The pair will meet on Sunday for the sixth time in a grand slam final, when world number one Federer will be looking for a modern-era record of six consecutive Wimbledon titles and world number two Nadal for his first at the All England Club.

While Federer leads the way on grass, Nadal is streets ahead on clay, having sealed his fourth successive French Open title last month after a rout in which he allowed the Swiss just four games.

"He's made me improve, you know, just the approach, playing against him," Federer told a news conference.

"He's challenged me, especially on clay for me. I don't know how much he's helped me to play against other players. But I definitely feel like he's made me more tough, that's for sure."

They will meet for the final on Centre Court for the third year in a row, with Federer well aware that Nadal would love to snatch the grand slam title on the Swiss's favourite surface in the same way that he was hoping to win the one on clay.

"I'm very happy with my run in Paris. He's probably very happy with his run here in Wimbledon. We want a piece of each world, you know but the other person hasn't given in yet," said the 12-times grand slam title winner.

"I think it's a great rivalry."

Federer admitted he used to get annoyed when Nadal, who notoriously takes his time before serving, dithered between points but said the Spaniard appeared to have quickened his pace of late.

"It used to be irritating ... I think he's speeded it up actually a little bit since those times. I actually felt like he was playing fair, you know," said the Swiss.

"He does still play slow but not as slow as maybe eight matches ago when I played him. I don't think I win or lose a match because he takes five seconds extra per point. That's not going to kill me."

(Editing by Clare Lovell)