Scotland's Russell Knox fired a bogey-free nine-under-par 63 to seize the lead in Thursday's opening round of the PGA Safeway Open, the first round of the 2020-21 season.
Knox's round was the lowest in the first 18 holes at the Silverado Country Club in Napa, California, since Scott Piercy's 62 in 2016.
Brendan Steele was second on 65 with fellow Americans Scott Harrington, Tom Hoge and Akshay Bhatia plus China's Andy Zhang sharing third on 66 with half the field still on the course.
Knox seeks his third US PGA title after wins in 2015 at the WGC Shanghai event and in 2016 at the Travelers Championship.
The event was played with air quality monitoring and an orange haze in the sky due to wildfires burning in areas of Northern California.
After sinking an 11-foot birdie putt at the fourth, Knox reached the green in two at the par-5 fifth and sank a 14-foot eagle putt, then dropped his approach inside six feet at the sixth to set up another birdie.
Knox closed the front nine with a birdie putt from 2 1/2 feet then began the back side with a 10-foot birdie putt and dropped in another birdie from 31 feet at the 12th.
He closed with birdies at the par-5 16th and 18th holes, each from about four feet, to stand alone atop the leaderboard.
Knox hit 11 of 14 fairways and 14 of 18 greens in regulation and didn't miss a putt inside of 10 feet.