Choi, seeking her first LPGA Tour victory, ended 54 holes at 17-under-par 199, breaking Stacy Lewis' year-old 54-hole scoring record by three strokes at the Crossings Course.
Hot on her heels was Anna Nordqvist, who set a single-round course second with an 11-under 61 -- breaking the mark of 62 set Friday by Sydnee Michaels.
Nordqvist finished the day one shot behind Choi at minus-16, tied in second place with second-round leader Jessica Korda (69).
Alone in fourth place was Karrie Webb, who also carded a 69 to end 54 holes at minus-15.
Jennifer Johnson (65) held fifth at 14-under 202.