STUTTGART, Germany — Fourth-seeded Philipp Kohlschreiber reached the quarterfinals of the Mercedes Cup today by defeating Yuri Schukin 6-3, 6-3.

Kohlschreiber, who is Germany's top Davis Cup player, broke the Kazakhstan qualifier's first service game and took a 5-1 lead before winning in 80 minutes at the clay-court event.

"I want to still be in this event over the weekend," said Kohlschreiber, who hadn't reached the quarterfinals in three previous attempts.

The 35th-ranked Kohlschreiber next plays Juan Martin Del Potro, a 19-year-old Argentine who defeated sixth-seeded Simone Bolleli of Italy 6-3, 3-6, 6-3.

Jan Hernych of the Czech Republic beat Brian Dabul of Argentina 7-6 (5), 0-6, 7-6 (5) after having replaced defending champion Rafael Nadal when he pulled out with knee problems following his Wimbledon win.