Andrew Loupe was unable to complete his opening round but he was still two shots clear atop the leaderboard when bad light suspended play.
Darkness halted the first round in Silvis, Illinois on Thursday with Loupe through 14 holes at eight under.
Loupe - seeking his first win on the PGA Tour - lit up the golf course at TPC Deere Run, the American flawless as he birdied eight holes without dropping a shot before play was called off for the day.
Patrick Rodgers, Ryan Moore and Zach Johnson are all tied for second, alongside fellow American Tom Gillis, who was through 16 holes.
A stroke further back at five under are Scott Pinckney and Scott Brown, while Morgan Hoffman (through 14) and Geoff Ogilvy (through 12) are yet to complete their rounds.
Of the five players tied at four under, only one player finished their 18 holes - Bud Cauley.
Steve Marino (through 14), Vaughn Taylor (through 11), Ben Martin (through 12) and Zac Blair (through 11) will complete their rounds on Friday.
A total of 22 players are level at three under, though 10 were still in the middle of their rounds at the close of play.
Three-time winner Steve Stricker carded a one-under-par 70 to be seven shots off the pace, while 2014 champion Brian Harman is a stroke back.