STUTTGART, Germany -- World number two Rafael Nadal recorded his 90th win in 91 clay court matches to make the quarterfinals of the Mercedes Cup in Stuttgart at the expense of local hero Philipp Kohlschreiber.
Nadal grimaces as he battles with a knee injury at the event in Stuttgart.
But tournament favourite and top seed Nadal had to be treated for a knee injury early in his 6-3 6-3 win over the German and admitted he was concerned about his future matches in the tournament.
The Spaniard said it was a similar pain to the one he suffered in the final at Wimbledon this month, where he was beaten over five sets by Roger Federer.
"It was the same as in the Wimbledon final, I had a piercing pain in the knee and when it started, I really began to doubt if I could play on," said Nadal, who needed one hour and 40 minutes to round out his victory.
The Roland Garros winner is playing his first clay tournament since his Paris win and will now meet Argentinian eighth seed Juan Monaco in Friday's quarterfinal.
The biggest upset of the day came when third seed Tomas Berdych was dumped out of the second round in straight sets by Spaniard Feliciano Lopez, ranked 74 places below him, who took just over 50 minutes to beat the world number 10.
Having been white-washed 6-0 in the first set, Berdych, who won his only title of the year so far at Halle last month, rallied briefly in the second set but went down 6-0 6-3 to Lopez, who faces compatriot Juan Carlos Ferrero on Friday.
Monaco beat Austrian Stefan Koubek 6-2, 3-6, 6-3 while sixth-seeded Ferrero had a tough time beating Argentina's Diego Hartfield in three sets in just over two hours. E-mail to a friend