Ko, who became the youngest winner in LPGA Tour history when she won the 2012 Canadian event at age 15, finished this year's tourney at 15-under-par 265.
She became the first player in nearly two years to successfully defend an LPGA crown.
Karine Icher (67) finished second at 10-under.
Third-round leader Caroline Hedwall (71) and Brittany Lincicome (69) tied for third at 9-under.
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