Choi had a 12-under 204 total on the English Turn course, a stroke ahead of John Rollins (68) and Bryce Molder (69).
Molder, a four-time All-American at Georgia Tech who set the NCAA record for career scoring average (70.69), is trying to play his way onto the PGA Tour through sponsor exemptions.
First-round leader Dan Forsman had a 72, leaving him two shots off the pace at 10-under 206. Billy Andrade (68) was 9 under, and Chris DiMarco (70) topped a five-player group at 8 under.
Defending champion David Toms (71) was 7 under, and Phil Mickelson (71) was 6 under.
Eighty-one players, including leader Kelly Robbins, didn't even get on the course as rain forced LPGA Tourt officials to shorten the Chick-fil-A Charity Championship from 54 to 36 holes at Stockbridge, Ga.
Robbins shot an 8-under 64 on Friday. Karrie Webb, Se Ri Pak, Laura Diaz and Juli Inkster were 6 under. Pak completed seven holes in the second round, Webb played four holes and Diaz and Inkster did not start. Annika Sorenstam was 1 over after seven holes.
England's Malcolm Mackenzie, winless in 509 PGA European Tour starts, shot a 7-under 65 to take a one-stroke lead after the third round of the French Open at Versailles.
Mackenzie had a 14-under 202 total on Le Golf National's Albatross Course. Defending champion Jose Maria Olazabal of Spain and South Africa's Trevor Immelman were tied for second. Olazabal shot a 67, including an ace on the 208-yard second hole. Immelman had a 71.
Larry Nelson shot two 6-under-par 66s to take a one-stroke lead over defending champion Hale Irwin in the rain-soaked Bruno's Memorial Classic at Hoover, Ala.
Irwin birdied the final four holes and tied a tournament record with his second-round 63. He played 24 holes Saturday.
Sammy Rachels and George Archer were two strokes back at 10 under. Rachels birdied six of his final seven holes for a second-round 64. At 62, Archer looked anything but his age with a pair of 67s and no bogeys in the first two rounds.
-- From wire reports