Fabio Fognini joined an early exodus of the seeded players at the Generali Open on Thursday, losing to 303rd-ranked Marc-Andrea Huesler 6-1, 6-2 in the second round.
The top-seeded Italian, who is ranked 12th, had a bye in the opening round and played his first match since undergoing arthroscopic surgery on both ankles in May.
Fognini double-faulted four times and won just eight points on serve before dropping the opening set against the Swiss qualifier in 22 minutes.
Huesler saved three break points early in the second set and held serve throughout before wrapping up the victory with a forehand winner.
It was only the third career win on the ATP tour for Huesler, who will meet Feliciano Lopez in the quarterfinals.
Fogninis defeat made No. 2 Diego Schwartzman the only seeded player left in the tournament.
The 13th-ranked Argentine took the last three games against Austrian wild-card entry Sebastian Ofner to close out a 6-2, 2-6, 7-5 win.
Earlier Thursday, No. 3 Dusan Lajovic, No. 4 Nikoloz Basilashvili, No. 5 Hubert Hurkacz and No. 7 Guido Pella all went out.
The clay-court tournament against a backdrop of the Austrian Alps is the first ATP event in Europe since February.