Knost leads Zach Johnson by three shots heading into Sundays final round. Two-time champion Boo Weekley is a shot further back, while defending champion Brandt Snedeker, Kevin Na and Robert Garrigus are six shots off the lead.
World No. 1 Luke Donald is T-52, 14 shots behind Pettersson. He must finish inside the top 8 to maintain the No. 1 position in the Official World Golf Ranking.