Geneva, Switzerland (SportsNetwork.com) - U.S. Open champion Marin Cilic suffered a quarterfinal upset Thursday at the Geneva Open, a final clay- court French Open tune-up.

Colombian clay-courter Santiago Giraldo dismissed the second-seeded Croatian star Cilic 7-5, 6-3 at Geneva Tennis Club.

Giraldo's semifinal opponent on Friday will be fellow South American Thomaz Bellucci, as the Brazilian snuck past Spaniard Albert Ramos-Vinolas 6-0, 1-6, 6-3 on Day 5.

Another quarterfinal result saw sixth-seeded rising Portuguese Joao Sousa oust third-seeded Spaniard Pablo Andujar 6-4, 2-6, 7-6 (8-6).