The 26th-ranked Stosur, a former
Before Strasbourg, where she won a seventh career title, Stosur had won only eight matches in 2015.
The Australian dropped her serve twice in the opening set but was at her defensive best in the following sets, saving all five break points she faced.
Dominic Thiem held his nerves to win his first
The 21-year-old Thiem, who defeated second-seeded
It was Thiem's second tour final after losing to David Goffin last year in Kitzbuhel.
The 27-year-old Bellucci's fourth career ATP title was his third in Switzerland. He also won on clay at the Swiss Open in Gstaad in 2009 and 2012.
Bellucci, a 60th-ranked left-hander, wasted three set points at 5-4 in the first before winning the tiebreaker.
He trailed by a service break in the second then reeled off four straight games to complete the victory.
Karin Knapp defeated fellow Italian
The sixth-seeded Knapp forced 17 break points and converted seven — three of those in the final set — to beat her fourth-seeded compatriot in 2 hours, 6 minutes.