Defending champion Tommy Haas advanced to the quarterfinals of the Gerry Weber Open on Thursday by outlasting Ernests Gulbis 7-6 (5), 6-4.
Second-seeded Richard Gasquet defeated Jurgen Melzer 6-3, 6-1, and Philipp Kohlschreiber stopped Tobias Kamke 6-4, 6-3 to reach the final eight in the grass-court tuneup for Wimbledon.
The 35-year-old Haas, who won the event in 2009, is coming off a quarterfinal appearance at the French Open.
The oldest player in the top 100, Hass is aiming for his second title of the year. The 11th-ranked German won last year's title by beating Roger Federer.
On Friday, Haas will face Gael Monfils, while the top-seeded Federer will play Mischa Zverev.
Kohlschreiber will take on Mikhail Youzhny, and Gasquet will face Florian Mayer, who beat Gasquet at Wimbledon last year.
"He returns very well, he doesn't give you much space to maneuver him around the court," Gasquet said of Mayer.
The Frenchman was pleased with his match after a bye into the second round.
"I served big and I returned well," said Gasquet, who landed 88 percent of first serves. "The grass here is faster than in England."