Geneva, Switzerland (SportsNetwork.com) - Heavy Swiss crowd favorite Stan Wawrinka and U.S. Open champion Marin Cilic both suffered quarterfinal upsets Thursday at the Geneva Open, a final clay-court French Open tune-up.

Argentine Federico Delbonis came from behind to stun the top-seeded former Aussie Open champ Wawrinka 6-7 (5-7), 6-4, 6-4, while Colombian clay- courter Santiago Giraldo dismissed the second-seeded Croatian star Cilic 7-5, 6-3 at Geneva Tennis Club.

Up next for Delbonis will be sixth-seeded Portuguese Joao Sousa, while Giraldo's semifinal opponent on Friday will be fellow South American Thomaz Bellucci, the Brazilian left-hander who snuck past Spaniard Albert Ramos- Vinolas 6-0, 1-6, 6-3 on Day 5.

Sousa ousted third-seeded Spaniard Pablo Andujar 6-4, 2-6, 7-6 (8-6).