The Italian, seeded third at the tournament in Dallas, ended her preparations for next week's US Open in perfect style, sealing victory in just over two hours.
It was the 29-year-old's seventh career WTA title, but her first since winning in Budapest in 2011.
Vinci struggled on her serve, but Serb Jankovic - also seeking her first title of the year - failed to capitalise, dropping to 1-3 in career meetings with the Italian.
Victory for Vinci improved her record in finals to an impressive 7-1.
She kicks off her US Open campaign at Flushing Meadows against Urszula Radwanska while Jankovic plays Kateryna Bondarenko first up.