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.

Australian Cameron Percy, who closed with three consecutive birdies, and Americans Sam Burns and Bo Hoag shared second on 64 with Americans Brendan Steele and Pat Perez on 65 when play was halted by darkness.

The 15 players still on the course when play was halted will finish their opening round Friday morning before starting their second round.

The event, delayed by an hour for morning fog, was played with air quality monitoring and an orange haze in the sky due to wildfires burning in areas of northern California.

Knox seeks his third US PGA title after wins in 2015 at the WGC Shanghai event and in 2016 at the Travelers Championship.

The 35-year-old Scotsman was two spots shy of making the 2019-20 PGA season-ending playoffs, but worked hard ahead of his return this week.

"I've worked as hard as I ever have the last two weeks before this event, so it's really nice to see something good happen immediately," Knox said. "I definitely feel like my game is heading in the right direction."

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.

Leading scores after Thursday's first round of the US PGA Tour's Safeway Open at Silverado Country club in Napa, California (par 72, USA unless noted, halted by darkness with 15 players to finish round on Friday):

63 - Russell Knox (SCO)

64 - Sam Burns, Cameron Percy (AUS), Bo Hoag

65 - Brendan Steele, Pat Perez

66 - Tom Hoge, Scott Harrington, Akshay Bhatia, Andy Zhang (CHN)

67 - Stewart Cink, DJ Trahan, Tim Wilkinson (NZL), Brian Stuard, Patrick Rodgers, Carlos Ortiz (MEX), Charley Hoffman, Chez Reavie, Harold Varner