Robert Streb kept his game from coming undone and then pieced together enough birdies to build a three-shot lead going into the final round of the PGA Tour's RSM Classic.

Streb came from five shots behind when he won at Sea Island six years ago, his only PGA Tour title.

This time, his 3-under 67 on moving day has him at 17-under par and in the lead from two-time major winner Zach Johnson (65) and Bronson Burgoon (67).

Camilo Villegas pulled within one shot on the lead going to the back nine of the Seaside course until a two-shot swing at the 10th cost him momentum.

Streb hit his approach close for birdie while Villegas was just on the fringe 15 feet away, ran it by five feet and missed that to fall three shots back.

Colombian Villegas added a bogey on the 13th, didn't make a birdie on the back nine and had to settle for a 70.

He was five shots behind as he tries to win for the first time in five years, and after a summer in which his 2-year-old daughter died of tumours on her brain and spine.

Streb had to earn back his full PGA Tour card a year ago, and then missed the PGA Tour post-season for the third straight year.

He kept his status because of the pandemic-shortened year, and a victory on Sunday would give him an exemption through August 2023.

Argentine Emiliano Grillo had a 65 and was four shots off the pace while Kevin Kisner (66) and Kyle Stanley (68) are alongside Villegas tied for fifth.

Former world No.1 Jason Day was the leading Australian in a share of 14th at 9-under, after a 67 that included four birdies and a bogey, with his compatriots Aaron Baddeley (69, 6-under) and Matt Jones (70, 4-under) further back.

Streb avoided any bogeys despite some errant shots in the front nine to mainain his place at the top.

"It wasn't the greatest start but got out of there with a bunch of pars and tried to find some consistency and it got better," Streb said.