t was the 11th-ranked Russian's second title of the year, and ninth of her career, after a victory in Cincinnati in August. Petrova, 26, also was a finalist last month at Stuttgart.
Mattek, ranked 43rd, settled for a runner-up finish after reaching her first WTA final. The 23-year-old American made semi-final runs as Los Angeles and Birmingham as she reached the top 50 in the rankings for the first time.
The American offered the first real resistance that Petrova had faced all week.
After pocketing the first set, Mattek went up a break in the second, but Petrova held her nerve and gradually asserted herself.
"Bethanie made it so difficult for me today," Petrova said. "I really had to work hard.
"The four-all game in the second set was probably the key moment of the match. It was important I won it. I'm happy how I finished in the third set."
The tournament was the last on the regular WTA schedule. The tour season ends next week with the $4.5 million Tour Championships at Doha.
