Lewis, who entered the final round with a six-stroke lead, finished the tournament at 12-under 201.
After also winning the Mobile Bay LPGA Classic in April, Lewis has recorded seven Top-10 finishes overall and will grab the world No. 3 spot when rankings are released Monday, supplanting Cristie Kerr.
Taking second place was Katherine Hull (68) at minus-eight, while Azahara Munoz (69) and Mika Miyazato (68) ended in a third-place tie at 7-under.
Gal Gadot cast as Wonder Woman for 'Batman vs. Superman'
Beyonce flaunts bikini body, Blue Ivy in vacation pics