Top-seed Janko Tipsarevic opened his campaign at the Munich ATP claycourt tournament on Thursday by easing into the quarter-finals with a 6-4, 6-2 victory over Slovenia's Grega Zemlja as four Germans reached the last eight.
The Serbian, ranked 10th in the world, is aiming to clinch his second title of the year, having started the season with a win in Chennai.
Tipsarevic, who captured his first clay title in Stuttgart in 2012, will now play Germany's Daniel Brands, who beat French wildcard Gael Monfils 6-3, 3-6, 6-0, for a place in Saturday's semi-finals.
Veteran Tommy Haas takes on compatriot Florian Mayer in the only all-German quarter-final after the 35-year-old beat Latvia's Ernests Gulbis 6-4, 6-7 (3/7), 6-1 on his 10th appearance in Munich.
"It was a tough match, but I knew it would be beforehand," said Haas as rain-affected Thursday's play.
"It's perhaps my last big chance to win here."
Mayer, the sixth-seed and 2011 runner-up, rallied past Australia's Marinko Matosevic 2-6, 6-4, 6-2.
In the other quarter-final, fifth-seed Alexandr Dolgopolov will face Croatia's Ivan Dodig.