SAN FRANCISCO (AFP) - American Tyler Duncan fired a six-under 66 to take a one-shot lead at the halfway stage of the US PGA Tour's Safeway Classic on Friday.

The 28-year-old, who turned professional in 2012, had an erratic second round. But an eagle on the ninth hole helped offset a string of three consecutive bogeys at the Silverado Resort and Spa in Napa, California.

Duncan, who began the day tied for first, had a two-day total of 13-under 131, a stroke ahead of defending champion Brendan Steele, who shot a 67.

The tournament is the opener of the 2017-18 PGA Tour schedule.

Duncan began the day at the 10th hole. He had three birdies on his front nine, but then had three straight bogeys coming in, at the third, fourth and fifth.

He righted himself with birdies at seven and eight before an eagle at his final hole, the par-five ninth.

Steele had a bogey in his round, but he offset that with six birdies.

Chesson Hadley shot the best round of the day, firing an 11-under 61 that left him alone in third place on 133.

Hadley, who had lost his PGA Tour card at the end of the 2016 season, carded 10 birdies, a bogey and an eagle to put himself in the hunt going into the third round.

Zac Blair with a 66 and Tony Finau after a 65 were tied for fourth, two strokes behind Hadley on 135.

It was a further stroke back to Graham DeLaet of Canada and Brian Davis of England, DeLaet carding a 67 and Davis a 66 for 136.

Five-time Major winner Phil Mickelson signed for a 69 and was tied for 15th on 138.