The local favorite, former North Carolina State player and member of the tournament's board had three birdies during a four-hole stretch on the back nine, finished at 21-under 259 and earned $918,000.
Scott McCarron, who briefly led midway through the final round, shot a 68 and to finished second. Rich Beem's second straight 63 left him four strokes off the lead, with J.J. Henry (62) and rookie Martin Laird (63) another shot behind him.
But there was never any question that the last day of the PGA Tour's final pre-playoff event was anything but a two-man showdown, with the Swede making his move immediately after he slipped out of the lead for the first time since early in the second round, when he shot a tournament-record 61.
Pettersson began the back nine with consecutive bogeys and fell one stroke back to 19 under when he missed an 8-foot par putt on the 10th.
But McCarron gave the stroke back on the next hole, missing a 13-foot birdie putt, lipping out a 4-foot par attempt and recording just his second bogey of the tournament.
Pettersson birdied the 13th for a one-stroke lead, then went back up by two shots with a birdie on the par-5 15th — the easiest hole on the course for everyone but him, after two bogeys and a par on it. This time it was McCarron's turn for trouble; he sent his second shot into the sand, recovered and lipped out an 8-foot birdie putt.
McCarron's bogey on the 17th all but locked up Pettersson's first victory since the 2006 Memorial.
McCarron — who had used two early birdies to erase the two-stroke lead that Pettersson brought into the round — was denied his fourth career victory and first since 2001. It was the second top-10 finish of the year for the PGA Tour veteran who sat out the 2007 season after having surgery to repair a tendon in his right elbow.
Beem and Henry both finished strong and propelled themselves off the FedEx Cup bubble and into the playoffs, which begin later this week at The Barclays.
Beem had birdies on four of his last six holes, jumping 52 spots to 114th, while Henry, who birdied four of his final five holes, moved up 42 spots to 135th. Laird, who shared the first-day lead with Bob Heintz before falling off the pace, wound up jumping 36 spots to 128th.