Lewis ended Saturday's second round two shots behind Ai Mayazato, then after play concluded was slapped with a two-stroke penalty for having her caddy testing the surface of a bunker.
But Lewis roared back Sunday to claim the victory at JW Marriott Phoenix Desert Ridge Resort & Spa, posting a three-shot win at 23-under-par 265.
Miyazato tumbled to a 1-under 71 in the final round, ending at 20-under 268.
Claiming sole possession of third place at minus-17 was Angela Stanford (68).
Jessica Korda (66), Giulia Sergas (68), Lizette Salas (69) and Jee Young Lee (71) shared fourth at 16-under.