US PGA Tour rookie Tyler Duncan fired a one-under par 71 on Saturday to maintain a one-stroke lead in the Safeway Open in Napa, California.
Duncan countered four bogeys with five birdies on the North Course at Silverado Resort and Spa to build a 54-hole total of 14-under par 202.
That kept him one shot in front of Chesson Hadley, who followed up his second-round 61 with a two-under 70 for 203.
Hadley had three of his four bogeys on the front nine but found six birdies on the day to keep the pressure on Duncan.
Bud Cauley climbed the leaderboard with a 66 for 204, sharing third place with Brendan Steele (72).
Steele started the day one shot off the lead but his two birdies were balanced by two bogeys.
Argentina's Emiliano Grillo and Canadian Graham DeLaet were a further stroke back on 205.
Five-time major champion Phil Mickelson headed a group on 206, alongside Andrew Putnam, Bill Haas and Tony Finau.
Mickelson, who hasn't won since his 2013 British Open triumph, strung together four straight birdies from the fourth through the seventh holes.
He had seven birdies overall to put himself in contention in the first tournament of the US PGA Tour's 2017-18 season.
John Daly made the cut and shot a 71 Saturday to give him a three-round total of 214.