It is the 10th career win for No. 16-ranked Vinci in a WTA singles final and snaps a 0-4 streak in finals dating back to 2013 and including last year's US Open, where she lost to fellow Italian Flavia Pennetta.
A to-and-fro first set saw Vinci broken twice as she landed just 51 percent of her first serves, but the Italian responded with three breaks of her own.
Vinci then held serve throughout the second and broke Swiss 18-year-old Bencic once to win in 1 hour, 19 minutes.
Despite her defeat in the final, the 11th-ranked Bencic is set to rise into the WTA top 10 for the first time Monday.