The Texan shot 6-under 66 on Friday to take a two-stroke lead over Carl Pettersson after the second round. Knost, tied for the first-round lead with Chad Campbell and Evans resident Vaughn Taylor after 67, had three birdies in a four-hole stretch midway through the round and finished at 9-under 133.
Pettersson had 65, his best ever showing in 32 career rounds at Harbour Town Golf Links. Two-time RBC Heritage winner Boo Weekley (66) and former Georgia golfer Harris English (68) were another shot off the lead at 6-under.
Campbell (70) and Robert Garrigus (66) were four shots behind.
Taylor, who got in the field on a sponsor exemption, followed his opening 67 with 73 and dropped into a tie for 16th place, seven shots behind Knost.
The 26-year-old Knost was one of the fastest risers in golf a few years ago, winning the U.S. Amateur, the U.S. Public Links championship and helping the American team win the Walker Cup in 2007. He won twice on the Nationwide Tour in 2008.
“I felt like I was ready for this level out here,” Knost said. “And apparently, I wasn’t.”
Knost missed the cut in 13 of 24 tour events that year and earned just $180,734 to lose his card after 2009. He regained playing privileges after another season on the Nationwide Tour and yet again struggled at the higher level, missing cuts in 15 of 26 events. Knost held on to his tour card at Q-school last year.