Choi ended at 14-under 274 for her second career LPGA Tour win following her triumph at this year's U.S. Women's Open.
She recorded a pair of birdies on the back nine to secure the victory.
First-round co-leader So Yeon Ryu was tied with Choi on the 14th hole but then bogeyed the next and ended up carding a 70 as well that left her in second place at minus-12.
Ai Miyazato began the day one shot off the lead but stumbled to a 74 to end up in fifth at 9-under.
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