Tsonga beats Mahut to advance at Hamburg Masters

Nadal has complained that the European clay-court season has been crammed together this year without a week off between any of the tournaments.

"After Rome, I had to come here," said Nadal, conceding that he might have skipped Hamburg if he had lasted until the final in Rome.

"Four straight weeks on clay, that is too much," said Nadal, who won the tournaments in Monte Carlo and Barcelona before going to Rome.

Nadal may be the dominant player on clay but it's Federer who rules in Hamburg. Nadal has played in Hamburg only twice before, and lost last year's final to Federer, who ended Nadal's 81-match winning streak on clay.

Federer has won the Hamburg event four times and his first victory came in 2002, when he broke into the top 10.

"I've done particularly well here and I always play unbelievable tennis in Germany," Federer said.

Federer has had a troubled season so far, after having mononucleosis at the start of the year. His only title came at a relatively small clay-court event in Estoril last month.

The loss in Rome was his sixth of the year, but Federer said he wasn't feeling more vulnerable.

"It's a distorted picture, because this year I am focusing more on the Masters Series and the Grand Slams and I am not playing so many events," Federer said. "I feel I am moving well, playing my normal tennis again.

"I was unhappy with the way I played in Rome, but it happens sometimes. I have to make sure it doesn't happen too often," Federer added. "The more you lose, the more they believe they can beat me. But believing is not enough, you still have to beat me."

Federer said he would start worrying if he didn't do well at the upcoming Grand Slams, the French Open, which he has never won, Wimbledon and the U.S. Open.

"Then, it would be a different situation," said Federer, who needs two Grand Slam titles to pull even with Pete Sampras, who had 14.