Second seed Juan Monaco was an easy second-round winner, while his fellow seeds Bernard Tomic and Tommy Haas were upset victims Thursday at the Mercedes Cup tennis event.
The Argentine Monaco whipped German Tobias Kamke 6-2, 6-3 on the red clay at TC Weissenhof. Monaco's quarterfinal opponent on Friday will be Slovakian qualifier Pavol Cervenak.
Meanwhile, Brazil's Thomaz Bellucci doused the third-seeded Aussie Tomic 7-6 (8-6), 6-3 and Cervenak surprised the eighth-seeded long-time German favorite Haas 6-4, 6-4 on Day 4.
Last month, on his home soil, Haas stunned Wimbledon champion Roger Federer in a grass-court finale in Halle.
One final second-rounder Thursday saw German Cedrik-Marcel Stebe best Frenchman Jeremy Chardy, the 2009 Mercedes Cup champ, 4-6, 7-6 (10-8), 6-3.
Friday's other quarterfinals will pit top-seeded Serb Janko Tipsarevic against German Bjorn Phau, Bellucci versus Stebe, and German Dustin Brown against Spaniard Guillermo Garcia-Lopez.