Swede Nordqvist had a run of five birdies starting on the third and added an eagle on the 13th on The Crossings course at the Robert Trent Jones Golf Trail's Magnolia Grove complex.
''Today was a lot of fun,'' she said. ''I started out with a couple birdies, hit a lot of good shots, and I think I missed one green.''
Choi shot her second straight 66 to take a one-stroke lead over Jessica Korda and Nordqvist, who is seeking her first win since capturing the LPGA Championship and season-ending LPGA Tour Championship as a rookie in 2009.
Choi twice made three straight birdies to move to 17-under-par as she seeks her maiden LPGA Tour win.
Korda, the halfway leader, shot a 69. The American had a double bogey on 12 but rebounded with a 33-foot eagle putt on the 16th.
Defending champion and world number two Stacy Lewis is four strokes back after jumping up the leaderboard with a 63.