Top seed Rafael Nadal [Images] expects a real fight to extend his 33-match clay-court winning streak when he meets Argentine Gaston Gaudio, one of his few peers on the surface, in Sunday's Mercedes Cup final.

Spaniard Nadal has already won seven titles on clay this year, including the French Open, and eased through to the final here with a 6-2, 7-5 triumph over unseeded Finn Jarkko Nieminen.

But third seed Gaudio, Roland Garros champion last year, has won four times on clay this season and will be relatively fresh after his semi-final opponent Nikolay Davydenko of Russia [Images] was forced to retire, complaining of illness when trailing 3-6, 1-2.

"I think Gaudio and I are among the best players in the world on clay so it will be a good match," the 19-year-old Nadal told reporters.

"It's a nice final. It's going to be difficult for him and difficult for me. He is playing well, he won in Gstaad last week and he's made the final again.

"I'll have to play my best tennis to win."

Gaudio has beaten Nadal three times out of four but the Spaniard won their most recent match in Monte Carlo this year.

Nadal has been near the peak of his game all week, reaching the final without dropping a set, and Gaudio knows he will have to be at his clinical best to stand a chance.

"No one has managed to find the shot to bother him this week," the Argentine said after beating second seed Davydenko.

"He's going to be the favourite in the final, no doubt. Mentally he is so strong. I think that's the best part of his game."