Pettersson had a run of five consecutive birdies on the front nine and finished with a birdie on the 18th hole for 5-under-par 66 and a one-stroke lead over Knost heading into the final round.
Pettersson and Knost chatted and laughed throughout the round, looking more like a pair of duffers at the local muni out for a weekend round rather than pro golfers chasing a PGA Tour title.
“Two fat guys played in three hours, 48 minutes,” Pettersson said with a smile. “That was pretty good. But we had a good time.”
Zach Johnson, the 2007 Masters Tournament winner, shot 66 to move to third at 8- under, three behind the leaders.
Two-time RBC Heritage champion Boo Weekley had 70 and was in fourth another shot behind.
Defending champ Brandt Snedeker (69), Kevin Na (70) and Robert Garrigus (70) were next at 6-under.
CHAMPIONS TOUR: In Lutz, Fla., Michael Allen shot 4-under-par 67 to take a five-stroke lead after the second round of the Champions Tour’s Encompass Insurance Pro-Am.
Allen won the 2009 Senior PGA Championship for his lone victory on the 50-and-over tour.
Bernhard Langer, Sandy Lyle, Corey Pavin and Olin Browne are tied for second. Langer and Pavin shot 71, Lyle had 69, and Brown 66.
EUROPEAN TOUR: In Kuala Lumpur, Malaysia, a thunderstorm suspended play at the Malaysian Open for the second consecutive day, with Louis Oosthuizen holding on to a one-shot lead halfway through his third round.
The Masters runner-up birdied the 10th hole to move to 13-under at the Kuala Lumpur Golf and Country Club before play was stopped for the day on Saturday.
Stephen Gallacher of Scotland was a shot behind after completing 11 holes, while Pablo Larrazabal (67) is the clubhouse leader at 7-under-par 209.
NATIONWIDE TOUR: In Hayward, Calif, former Clemson golfer Ben Martin fell off the pace as the field finally completed the second round in the weather-delayed TPC Stonerae Championship.
Martin, who was the first-round leader after 65, shot 75 in the second round and is at 140.
He’s six shots behind the three 36-hole leaders – Paul Haley II (66 on Saturday), James Nitties (66) and Michal Putnam (68).
Augusta’s Scott Parel (74-70) and Aiken native Matt Hendrix (72-72) missed the cut by a shot.
The third round will be completed this morning, followed by the final round.