Scott Piercy fired a course-record 10-under 62 to take a two-shot lead at the Safeway Open on Thursday.
Piercy opened the PGA Tour season in fine fashion, holing 12 birdies in an incredible round at the Silverado Country Club.
The American holds the lead from Englishman Paul Casey (64) and Patton Kizzire (64).
Piercy had six birdies on his opening nine holes in Napa, California, and another before his first blemish at the par-four third.
He completed his round with five birdies in six holes.
Casey and Kizzire went through bogey-free, the latter making six birdies on the back nine.
American duo Johnson Wagner and Kyle Stanley are tied for fourth at the event, which was expected to be headlined by Tiger Woods before his withdrawal.
Spaniard Jon Rahm is at six under and provided the highlight of the day with a hole-in-one at the 182-yard 11th.
He had a mixed round otherwise, and sits alongside Troy Merritt and Bill Haas in a tie for sixth.
A group of six players are a shot further back, including Scot Martin Laird and Brendan Steele.
Despite making an albatross from 251 yards on the 18th, Morgan Hoffmann is at two under.
Defending champion Emiliano Grillo made a decent start as he opened with a three-under 69, as did Phil Mickelson.