Australian left-hander Nick O'Hern fired consecutive birdies on his final two holes to forge a one-shot lead in the opening round of the Reno-Tahoe Open in Nevada on Thursday.

O'Hern, who has yet to win a PGA Tour title, fired a sparkling seven-under-par 65 to take charge in bright sunshine at Montreux Golf and Country Club in Reno.

Chris Riley was alone in second after carding a seven-birdie 66 with fellow Americans Blake Adams, Briny Baird and 2006 winner Will MacKenzie a further stroke back after matching 67s.

O'Hern, best known in the U.S. for twice beating Tiger Woods in the early rounds of the WGC-Accenture Match Play Championship, made the most of ideal scoring conditions after teeing off in the first group of the day.

"I got nine very, very fresh greens and smooth greens, which is nice," the 39-year-old told reporters.

"The back nine they started to get a little bumpy but I played beautiful on the front nine.

"Can't play much better than that. I hit a lot of good shots and missed a couple of putts, but every time I hit an ordinary shot I got it up and down for par, so I kept the round going."

American Matt Bettencourt, who clinched last year's title by one shot, withdrew from Thursday's opening round because of a rib injury.

He had birdied two of his first four holes but then bogeyed the 16th and 17th, his seventh and eighth holes of the day, before deciding to pull out.

Most of the PGA Tour's biggest names are competing this week in the third World Golf Championship event of the year, the WGC-Bridgestone Invitational at Firestone Country Club in Akron, Ohio.