Defending champion Brandt Snedeker fired a seven-under par 65 to share the first-round lead with South Korea's K.J. Choi at the Farmers Insurance Open at Torrey Pines on Thursday.

Snedeker finished without a bogey on Torrey Pines' more forgiving North Course, while Choi had eight birdies and one bogey on the South Course.

Tiger Woods, making his US PGA Tour season debut in the $6.1 million event, emerged from an erratic round on the South Course three off the lead on 68.

Snedeker and Choi were one stroke in front of a group of eight players sharing third place on 66. Former Masters champion Mike Weir of Canada headlined the group, which also included England's Ross Fisher and American Charles Howell -- who lost in a playoff on Sunday at the Humana Challenge.

Canadian Adam Hadwin, Billy Horschel, Josh Teater, Luke List and Scott Stallings were also in the group at six-under.

Nine more players, including Bo Van Pelt and England's David Lynn, were tied on five-under 67.

Woods headlined another big group on 68 that also included Japan's Ryo Ishikawa, Fiji's Vijay Singh and South Korea's D.H. Lee.

Woods opened his 2013 season at the European Tour event at Abu Dhabi last week, missing the cut after taking a penalty for an improper drop.

On Thursday, he started promisingly with a birdie at the first on the South Course, where Woods won the most recent of his 14 majors at the 2008 US Open.

But Woods three-putted for a double-bogey at the par-four fourth. He responded with a birdie at the fifth and an eagle at the par-five sixth where he holed out from a bunker.

Woods had four more birdies before he was slowed again by bogeys at 15 and 17. "I made a few mistakes out there, but I made some nice plays as well," the former long-time world number one said.

Snedeker certainly wasn't counting out Woods. In addition to his US Open triumph in 2008, Woods has won the PGA Tour event at Torrey Pines six times, including four in a row from 2005-2008.

"I think he's won here more times than I've won on tour, so I think he knows the place pretty well," Snedeker said.

"He's very similar to me. He loves putting on these greens."

Ishikawa, the 21-year-old Japanese star playing his first full season as a PGA Tour member, had five birdies and a bogey on the North Course.

"I've done my goal today, so I'll focus on tomorrow," said Ishikawa, who recently bought a house in nearby Carlsbad, California.

Snedeker is one of the co-holders of the North Course record of 61.

After teeing off on 10, he birdied 14, then strung together four birdies in a row from the 16th through the first, then added back-to-back birdies at seven and eight for good measure.

"These greens bring out my best," Snedeker said. "I put in a lot of hard work yesterday on the putting green because I wasn't real happy with the way I was rolling it. I came out here today and rolled it the way I wanted to."

Choi's eight birdies included four in a row on the back nine and he played the four par-fives in four-under.