Bovina posted a 6-2, 2-6, 7-5 victory over Dechy at Yale to claim her first WTA Tour singles title since 2002 and the third of her career.
Bovina earned $93,000 for the tournament title. She is 3-1 in WTA finals, having also won in Warsaw and Quebec City.
Bovina, 21, had reached the final with a 6-1, 6-1 victory over French Open runner-up and second-seeded countrywoman Elena Dementieva. Dechy moved into the title match with a 6-4, 6-0 victory over American Lisa Raymond.
Dechy fell to 1-2 in her career against Bovina. She sought her second career title.
Bovina will be seeded 26th for the upcoming U.S. Open and meet Spaniard Marta Marrero in the first round. Dechy, 28th seed, faces Serbian Jelena Dokic.