Robert Streb leads The CJ Cup by one stroke following the opening round as American star Dustin Johnson struggled.
Streb carded a career-low 11-under-par 61 to set the early pace at The Summit Club in Nevada on Thursday.
The two-time PGA Tour champion joined Brandt Snedeker (2007 Farmers Insurance Open) as the only players to start a tournament at seven under in their first six holes (in the ShotLink era).
Streb made a red-hot start, having gone birdie-birdie-eagle-birdie-birdie-birdie in his opening six holes and while he bogeyed the 11th following the turn, the American reeled off another five birdies to close out the day.
"I've never had a start like that, so it was kind of fun," Streb said. "I was trying to stay in the moment as best I can and, I don't know, you just feel like you can start aiming at stuff. Things seemed to be going my way.
"Slowed down a little I guess in the middle, but it was a really, really good round. Even that bogey, I almost made the putt, so it just went really well."
Countryman Keith Mitchell is Streb's nearest rival, while Harry Higgs is three strokes off the pace at eight under heading into the second round.
Sergio Garcia, Viktor Hovland and Hudson Swafford are a shot further back, one stroke better off than Masters champion Hideki Matsuyama, former world number one Jordan Spieth and Rickie Fowler.
Four-time major winner and 2018 champion Brooks Koepka shot a first-round 67 to be within six strokes of Streb, while Rory McIlroy – featuring for the first time since his dismal Ryder Cup campaign for Europe – posted a four-under-par 68.
Justin Thomas, a two-time winner of the event, had to settle for an opening-round 69 as former world number one Johnson endured a forgettable two-over-par 74.
After a flawless front nine, which featured two birdies, Johnson capitulated with a double-bogey and three bogeys on the back nine.