Tour debutant Sepp Straka took a one-shot lead on the first day of the Safeway Open with a clean nine-under 63.
The Austrian led fellow rookie Chase Wright of the US in second, while Ryder Cup loser Phil Mickelson sat two shots off the pace in third at the Silverado Resort in Napa Valley, California.
Seamus Power is the sole Irish representative in the tournament but had a mixed round with five bogeys, four birdies and an eagle on the par-5 fifth round a round on 71 that leaves him on -1.
Straka, who earned his PGA card after finishing in third at the Web.com Tour Championship in September, hit nine of 14 fairways and 15 of 18 greens.
The Vienna-born 25-year-old picked up five shots by the 13th and hit back-to-back birdies from the 16th back to the clubhouse.
Putting defeat in France behind him, Mickelson shot a blemish-free round of 65 as the 2018/19 season got under way.
The three-time Masters champion fired off six of his seven birdies consecutively from the ninth.
Scotland's Martin Laird was four shots off the lead after carding a 67
