The 23-year-old Sydneysider shot a two-under-par 70 in the first round of the season-opening Safeway Open in California on Thursday in his first outing since graduating from the secondary Tour.

While Davis is in the top half of the field, it left him seven shots behind leader Sepp Straka of Austria, who was flawless with nine birdies on the North Course at Silverado Resort and Spa.

Davis is tied with countryman Brett Drewitt, who put his honeymoon on hold after securing a start from the Monday qualifying tournament.

Fellow Tour graduate Curtis Luck, 22, is a shot behind Davis after a 71, while veterans Matt Jones and John Senden lead the Australian contingent with 69s.

Luck opened with one-under 70 at the Safeway Open and is tied for 78th. PHOTO Robert Laberge/Getty Images.

Also newly-promoted from the Tour, Straka birdied the last three holes to lead by a shot from Chase Wright, with Phil Mickelson a further shot away after a 65.

Out of form during the Ryder Cup loss to Europe in Paris last week, Mickelson produced six straight birdies from the ninth hole but remained concerned by his golf.

I've been putting well, like I can putt," Mickelson said. "But I was surprised at some of the shots I've hit.

"Honestly, I hit it just terrible and today was kind of an anomaly. Don't let the good round fool you. I'm not at all at my best."

Brandt Snedeker, Alex Prugh, J.T. Poston, Mackenzie Hughes, Sam Saunders, Sungjae Im and Adam Long shot 66s.

Two-time defending champion Brendan Steele had a 67, playing alongside Mickelson.

Fred Couples, the Hall of Famer who turned 59 on Wednesday, had a 73 in his first PGA Tour round since the Masters in April.