Pettersson stood on 13-under par 197 after 54 holes with Canada’s Mike Weir and Australian Mark Hensby one stroke off the pace. Weir fired a 65 on Saturday while Hensby shot 66.
Hensby, currently 151st on the money list and battling to get into the top 125 and keep his playing privileges for next year, relinquished a share of the lead with a disappointing double-bogey at 18.
Aussie Jarrod Lyle was on 200 after a 64 of his own Saturday, tied with overnight leader Ryan Moore.
Japan’s Daisuke Maruyama and Americans Justin Leonard and Ben Crane were tied on 201.
Pettersson, who is gunning for his first title since he won The Memorial in 2006, also has the 2005 Chrysler Championship title on his resume.
But his best finish this year was fifth place, which he has accomplished three times.
Petterson, who started the day four strokes behind Moore, made a move early with three birdies in his first five holes.
“I only missed two greens and didn’t give myself any real opportunities to make bogeys,” said the player who is based in North Carolina. “I played steady, and I putted pretty good, too.”
Billy Mayfair started the day five shots adrift and picked up five birdies in his first 10 holes to forge a tie for the lead, but the American fell back with bogeys on four of his last six holes.
Mayfair finished with a 68 for 202, five shots off the lead. Meanwhile Moore, still seeking his first win as a pro after a stellar amateur career, endured an erratic round.
He countered three bogeys with two birdies through seven holes, then dropped a shot at two of his last three holes en route to a 71.