Justin Rose and Harold Varner III opened with seven-under 63s at the Charles Schwab Challenge as the PGA Tour season resumed.
Suspended in March due to the coronavirus pandemic, the PGA Tour got back underway without fans in attendance in Texas.
Rose and Varner both produced bogey-free opening rounds featuring seven birdies to hold a share of the lead.
Starting on the back nine, 2018 champion Rose made four birdies on his first seven holes before three straight from the first hole.
Varner holed four birdies on the front nine to set up his round as the American shared a one-stroke lead with Rose.
Justin Thomas, Jhonattan Vegas, Abraham Ancer and Collin Morikawa are tied for third at six under.
Thomas, the world number four, also went through bogey-free to be in early contention for his second win of 2020.
On what is a congested leaderboard, a group of nine players are a shot further back, including Bryson DeChambeau, Tom Lehman, Jordan Spieth and Xander Schauffele.
Lehman, 61, became the oldest player since 1980 to shoot 65 or lower on the PGA Tour.
Spieth, who has fallen out of the world's top 50, holed five birdies on the back nine to climb into a tie for seventh.
Rory McIlroy and Brooks Koepka managed two-under 68s in their opening rounds.
Despite a two-over 72 to start the tournament, Sung Kang produced one of the shots of the day with a hole-in-one at the 13th.