Defending champion Tommy Haas into Halle last-eight
He is making his 13th appearance at the pre-Wimbledon warm-up and took the title for the first time in 2012, beating Roger Federer in the final.
Defending champion Tommy Haas reached the quarter-finals of the Halle grasscourt tournament on Thursday beating Ernests Gulbis, 7-6 (7/5), 6-4, after the Latvian had saved 16 of 16 break points.
World number 11 Haas will face France's Gael Monfils for a place in the semi-finals.
"I knew that I had to play my best tennis to stay in the tournament," said Haas, of the challenge posed by world number 38, Gulbis.
"Gulbis is a great player who is on the up."
Haas is one of four German players to make the last-eight after Philipp Kohlschreiber, Florian Mayer and Mischa Zverev.
He is making his 13th appearance at the pre-Wimbledon warm-up and took the title for the first time in 2012, beating Roger Federer in the final.
French world number nine Richard Gasquet eased past Austria's Jurgen Melzer, 6-3, 6-1, and will face Mayer on Friday.
The German got the best of his Argentine namesake Leonardo Mayer, 6-2, 6-3.
Kohlschreiber, the 2011 champion, beat compatriot Tobias Kamke, 6-4, 6-3 and will take on Russia's Mikhail Youzhny.
Kohlschreiber has beaten his doubles partner Youzhny seven times in eight meetings, but they have never met on grass.
Federer will face Russian-born Zverev, the world 156.
Five-time Halle champion Federer has yet to win a title in 2013.