Miyazato, 22, fired three birdies and carded a single bogey to finish at 13-under 203 at Pumpkin Ridge Golf Club, entering the winner's circle for the first time following several near-misses.
This year she has been a runner-up at both the LPGA Championship and Arkansas Championship, and also garnered a co-third-place finish at the ShopRite LPGA Classic.
Following her in second place at minus-11 were Brittany Lincicome (67) and Inbee Park (69).
Knotted for fourth at 10-under 206 were Haeji Kang (66), Cristie Kerr (70) and So Yeon Ryu (71).
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