Argentine baseliner Guillermo Coria outplayed Spain's David Ferrer 6-1, 6-1 on Thursday to book a place in the quarterfinals of the Mercedes Cup.
Coria, seeded second in the 765,000 euro (US$858,900) claycourt event, played close to perfection in a third round match that started 90 minutes late because of rain.
The French Open semi-finalist, the highest seed left in the draw after top seed Carlos Moya of Spain bowed out on Wednesday, goes on to meet defending champion Mikhail Youzhny of Russia, who defeated Czech Jiri Novak 7-6 6-4.
The 21-year-old Coria, who won the Hamburg Masters and reached the final in Monte Carlo this year, improved his record on clay this season to 25-5.
Local favorite Rainer Schuettler, seeded third, followed Coria into the last eight with a convincing 6-4 6-4 win over Spaniard Alex Corretja.
Schuettler, this year's Australian Open runner-up, will continue his quest for a first title on German soil by playing Spaniard Feliciano Lopez, who moved past Moroccan Younes El Aynaoui 3-6 6-4 6-3.
Corretja, the 15th seed, had saved four match points in his second-round victory over Belgian Olivier Rochus on Wednesday but was never in contention against a determined Schuettler.
On a good day for German fans, the unheralded Tomas Behrend, who had knocked out Moya on Wednesday, kept going with a 6-4 6-4 victory over 13th-seeded Max Mirnyi of Belarus.
Behrend, who had never beaten a top 10 player before overcoming Moya, managed a break in each set and held his nerve to seal victory with a service winner on his first match point.
The Brazilian-born German will face Chilean Fernando Gonzalez, the sixth seed, who struggled to beat Finn Jarkko Nieminen 6-7 7-6 6-3 in a close contest that could have gone either way.