Choi -- who has gone on to win twice in the previous six times she has held 36-hole leads -- finished at 8-under-par 134, three strokes ahead of the competition.
Choi won two titles each in 2009 and 2010 but is seeking her first this year.
Stacy Lewis grabbed sole possession of second place with a 3-under 68, moving to minus-5 at Pumpkin Ridge Golf Club.
Mika Miyazato's 4-under 67 enabled her to climb 23 places into third place at 3-under 139, while Brittany Lincicome (68), Grace Park (73) and Ryann O'Toole (69) knotted for fourth at minus-2.
2014: The Year in Music [PHOTOS]