Defending champion Zach Johnson and Camilo Villegas have finished atop the leaderboard after the first round of the John Deere Classic.
The American shot a bogey-free round of 64 at Deere Run, while the only blemish on the Colombian's card came at the par-four ninth.
Brendon de Jonge, Matt Bettencourt and Daniel Summerhays are one shot further back on six-under-par.
Seven players are on five-under, while KJ Choi and Steve Stricker are among 13 challengers on four-under.
Johnson ended Stricker's three-year stranglehold on the title with victory in last year's event.
