South Korea's Whee Kim was one shot clear after posting a sparkling 65 on the opening day of the PGA Tour Shriners Hospitals for Children Open in Las Vegas.
The 25-year-old, after starting on the back nine, collected six birdies in a flawless first round at TPC Summerlin.
"That was really powerful," he said, quoted on pgatour.com. "I feel much more comfortable now. I'm trying to keep up that momentum. So still trying to work hard and I'm not going to change any plans for the next three days."
Germany's Alex Cejka was alongside Americans JJ Spaun, Ryan Blaum and John Huh in a tie for second place, with their compatriot Jimmy Stanger also on the five-under mark through 15 holes when play was suspended due to darkness.
An ace in Vegas? ♠️— PGA TOUR (@PGATOUR) November 3, 2017
He was THIS close. pic.twitter.com/7vYqYyJEoe
Stanger was one of 25 players still to complete the opening round and set to return early on Friday.
Waterford's Seamus Power was three under through 14 when play was halted, while Graeme McDowell signed for a round of one under par.
Presidents Cup team-mates Kevin Chappell and Charley Hoffman made solid starts on their season debuts, with rounds of 67 and 68 respectively.
Las Vegas resident Hoffman will donate his prize money from this week to victims of the recent mass shooting in the city, and will give a minimum of 20,000 US dollars regardless of whether he makes the cut.
"I want to play really well to raise some money," Hoffman said. "So my focus is way higher here than it has been in the past, which is sort of saying where my mind was at this time of the year the last few years.
"I've got a huge focus on trying to contend to win this golf tournament for the city of Las Vegas, and I know how much it means to them."
Double Masters champion Bubba Watson, looking to halt his slide down the world rankings, opened with a one-over-par 72 following an up-and-down round including four bogeys and three birdies.