Defending champion Robin Haase defeated Daniel Brands 6-4, 6-1 on Wednesday to stay on course for a third straight title at the bet-at-home Cup.
The 68th-ranked Dutchman saved all six break points against his serve and improved to 11-0 for the event. Brands, who beat Roger Federer in the second round at Gstaad last week, dropped his serve four times.
Second-seeded Juan Monaco defeated Austrian wild-card entry Andreas Haider-Maurer 6-3, 6-4. The Argentine, who won the event in 2007, came back three times from a break down in the second set.
In his seventh quarterfinal of the season, Monaco will play Daniel Gimeno-Traver, who defeated Jan Hajek 6-3, 6-3. Also, seventh-seeded Albert Montanes defeated Victor Hanescu 7-6 (2), 3-6, 7-6 (5).