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.
The Geneva Open returned to the ATP Tour after a 24-year gap, and replaced a tournament held in Duesseldorf, Germany.