The top-seeded Russian lost the opening set 6-4 before coming back 6-4, 6-1 against the sixth-seeded American.
"I won this mental battle,'' Petrova said.
The 140 points Petrova earned with this title will allow her to participate as an alternate in the year-end Sony Ericsson WTA Championship in Doha, Qatar.
In the doubles final, Germany's Anna-Lena Groenefeld and American Vania King topped Jill Craybas of the U.S. and Tamarine Tanasugarn of Thailand 7-6 (3), 6-4.
It was the second doubles title this year for both players.
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