American Williams came from 2-4 down in the opening set and then dominated the rest of the match with booming serves and hard groundstrokes to claim her first title since Wimbledon last year.
The 13-times grand slam champion, who returned to the tour in June after taking almost a year off due to injury and illness, triumphed for the first time on home soil since her victory at the 2008 U.S. Open.
After firing down a service winner to wrap up the match in one hour and 22 minutes, Williams skipped around the court in joyful celebration.
"I haven't won a tournament in forever that wasn't a grand slam so it's cool," said Williams, whose last non-major title was the 2009 WTA Championships in Doha.
"I put a lot of work into this week. I want to take this whole (hardcourt) swing serious. It's a good time for me."
