Feng broke away from a tight pack atop the leaderboard with a 5-under-par 67, firing the low round of the week en route to the historic win at Locust Hill Country Club.
She celebrated in the clubhouse after her final pursuers, Karrie Webb and Eun Hee Ji, failed to hole out from the fairway for eagle on No. 18, handing her the crown.
Feng finished at 6-under 282. Ji, the third-round leader, managed an even-par 72 to share second place two strokes back at minus-4.
Webb ended with an even-par 72, good for a three-way tie for third.