Luke Donald remained at the head of affairs at The Heritage as he continued his pursuit of the world number one ranking.
The 33-year-old is currently ranked number three but, with rankings leader Martin Kaymer having a week off and Lee Westwood playing in a tournament worth fewer ranking points in Indonesia, a win in South Carolina would move Donald to the head of the standings.
He made a tap-in birdie on the par-five second - a hole on which he acknowledges he has struggled this week, taking seven on Saturday.
He gave the shot straight back after driving into a bunker on the next but bounced back with two more birdies in succession to lead outright on 13 under having played six holes.
His nearest pursuer was Ricky Barnes after the young American birdied four of the first five holes to reach 12 under, having recorded back-to-back 67s on days two and three.
Barnes had the chance to move level with Donald but missed a short birdie putt at the eighth.
Compatriot Brandt Snedeker, meanwhile, recorded three birdies in a row from the second and six in total on the front nine as he surged to 11 under.
Yet another birdie followed on the 12th and, though he immediately blotted his copybook with a five at the par-four 13th, another birdie to follow left him just one shot behind Donald with four holes to play.
Jim Furyk was fourth on 11 under with Scott Verplank a further shot back, having both made solid if unspectacular starts in favourable scoring conditions.