Defending champion and top-seeded Mikhail Youzhny of Russia was one of three seeded players to tumble out of the BMW Open in the second round on Wednesday.
Philipp Petzschner of Germany upset Youzhny 7-6 (5), 3-6, 6-2 to avenge a semifinal loss to the Russian last year.
"My goal is to make at least the semifinals, like last year," said Petzschner, who reached his second quarterfinal of the year.
Bulgarian teenager Grigor Dimitrov reached his first career quarterfinal by rallying to beat fourth-seeded Marcos Baghdatis of Cyprus 3-6, 7-6 (6), 6-2.
Dimitrov, who is ranked No. 69 and will turn 20 next month, is the only teenager in the top 100.
Baghdatis snapped a six-match losing streak with his first-round win in Munich, where he was a semifinalist in 2007 and last year.
Potito Starace of Italy defeated sixth-seeded Sergiy Stakhovsky of Ukraine 6-4, 6-2 on a day of rain delays.
Starace will play Petzschner in the quarters.
Because of the delays, organizers moved the last second-round match between Florian Mayer of Germany and Teymuraz Gabashvili of Russia to Thursday.