Both players held their serve until the Estonian built a 40-0 lead in the 12th game of the second set before converting her first match point with a forehand winner.
It was her sixth win over a top-20 opponent this year.
Kontaveit didn’t lose a set on her way to the victory at the hard court tournament, her second title this season after also winning in Cleveland.
“It was such a good week for me,” Kontaveit said.
In her fourth final this season, Kontaveit hit 26 winners compared with 20 by Sakkari, who was playing in her first final since 2019.
She saved the only break point she faced in the final to reduce her overall record against her opponent to 5-6.
In the opening set, Kontaveit broke Sakkari in the fourth game to jump to a 4-1 lead and got another break in the eighth game to take it 6-2.