Choi had a two-shot advantage despite suffering a double bogey at the 18th hole of the Pumpkin Ridge Golf Club course that left her with a 6-under 65.
She birdied seven consecutive holes beginning at the par-3 fifth.
Grace Park was alone in second at 67 while LPGA Hall of Fame member Se Ri Pak shared third at 68 with Anna Nordqvist, M.J. Hur and Ashli Bunch. Stacy Lewis was among those who shot 69.
Choi is winless on the tour this year after having posted two victories in 2010.
World No. 1 Yani Tseng opened with a 72 while Cristie Kerr, ranked second, had a 73.