Knost has twice lost his spot on the tour and had to return to the PGA Qualifying tournament last year to regain his eligibility.
His 66 gave him a 36-hole total of 9-under 133 at the Harbour Town Golf Links. Carl Pettersson shot the low round of the tournament, a 65, to finish alone in second at 135.
It took a score of 3-over 145 to make the cut. Among those who survived was John Daly, making his second appearance on the tour this year.
Daly managed a 74 for a 144 total. World No. 1 Luke Donald was also at 144.
Among the big movers in the second round was Jason Dufner, who was a co-leader at the Masters after 36 holes last week. Dufner shot a 66 and climbed 67 places into a tie for 41st.
Matt Kuchar, who finished tied for third at the Masters, was at 141 after 36 holes.
Masters champion Bubba Watson did not play in this event.
Notable deaths of 2014 [PHOTOS]