Shortly after winning the 2007 U.S. Amateur, he turned professional, forfeiting his invitations to The Masters, the U.S. Open, and the Open Championship. Knost played in three events on the PGA Tour as a professional in 2007, making two of three cuts with his best finish coming at the Frys.com Open, where he finished T-38. Knost went to qualifying school to try to earn his PGA Tour card for 2008 but his finish of T-85 was not good enough to earn him his card.