Tyrrell Hatton shot 5 under through the opening five holes of the CJ Cup at Shadow Creek and tied the course record of 7-under 65 for a one-shot lead.
Dustin Johnson, not playing this week because of a positive test result for the coronavirus, had a 65 during a casual round in 2015.
Xander Schauffele birdied the par-5 18th for a 66 and was one shot behind, along with Russell Henley. Jon Rahm and Tyler Duncan were another shot behind.
Rory McIlroy bogeyed his last three holes, a streak that began with him missing a 3-foot par putt, for a 73.
Brooks Koepka, in his first tournament since taking two months off to heal an ailing left hip, showed plenty of signs of rust. He closed with a short iron into the water on the par-5 18th for a bogey and a 74.
Hatton was among six players outside London last week for the BMW PGA Championship, which the Englishman won on the course where he watched as a young lad and was inspired to play golf. So there was emotion, and then a 20-hour trip door-to-door to Las Vegas for a tournament that moved this year from South Korea because of the COVID-19 pandemic.
No one had a tougher day than U.S. Open runner-up Matthew Wolff, who didn’t make a birdie in his round of 80.
Jordan Spieth salvaged what could have been a rough day. He was so wild off the tee at times that he hit provisional tee shots on three consecutive holes. He didn’t have to use any of them, birdied three straight round the turn to get to 1 under only to hit a fourth provisional — this one he needed — in making a triple bogey on the 14th. He shot a 74.