Dominic Thiem crashed out of the Antalya ATP grass court tournament on Tuesday, the French Open semi-finalist stunned by India's Ramkumar Ramanathan, ranked 214 places below the world number eight.
The 22-year-old Ramanathan upset Thiem 6-3, 6-2 to claim the biggest win of his career.
Thiem made it into the French Open last four, beating Novak Djokovic in straight sets in the quarter-finals before losing to eventual winner Rafael Nadal.
However, he arrived in Turkey after a second-round loss to Robin Haase last week on grass in Halle.
The Austrian was appearing in Turkey to help prepare for the third Grand Slam of the year at Wimbledon which starts on Monday.
Ramanathan had only played in one ATP tour event this year before heading to Turkey, and that was at home in Chennai in January.