"In a racing situation I really have to be switched on much more than I have ever been on a golf course.
"On the fairways you can relax and take your time between shots but in a race car you can't afford to lose focus for a second or you're off the track."
Double US Open champion Lee Janzen, hunting his first PGA Tour victory in more than a decade, charged into a share of the lead in the opening round of the John Deere Classic in Silvis, Illinois.
The 44-year-old American fired a seven-under-par 64, which was matched by compatriot Darron Stiles.