Charles Howell III and Ollie Schniederjans opened with eight-under 63s to share the first-round lead at the John Deere Classic.
The American duo made bright starts at TPC Deere Run in Silvis, Illinois on Thursday to be top of a congested leaderboard.
Howell, the world number 56 who was runner-up at the Quicken Loans National, went through bogey-free.
Schniederjans, 24, was three under before making five birdies on his final eight holes.
The pair are two shots clear of Zach Johnson, Patrick Rodgers, Chad Campbell and South African Rory Sabbatini.
Johnson, a two-time major winner, mixed seven birdies with a bogey as he looks to add to his 2012 victory at the PGA Tour event.
The American is also a three-time runner-up, most recently in 2014.
A group of seven players are a shot further back at five under, including Wesley Bryan, Daniel Summerhays and Bryson DeChambeau.
Defending champion Ryan Moore made a poor start, shooting a three-over 74 to be tied for 129th.
Brian Harman, the 2014 winner, is at one under, while three-time champion Steve Stricker opened with a 73.