Lehman posted his score on the North Course at Torrey Pines Golf Club. Players rotate between the North and South Courses over the first two rounds before the final two are contested at the much more difficult South Course.
Dean Wilson is alone in second place after a 9-under 63 at the North Course. Arron Oberholser has sole possession of third after a 64, also at the North Course.
This event is the first battle of golf's 'Big Four' in 2005 as Phil Mickelson made his season debut. The only player in the top-5 in the Official World Golf Ranking not present this week is reigning U.S. Open champion Retief Goosen (No. 4).
Ernie Els, ranked third in the world, carded a 7-under 65 and is tied for fourth place.
'You've got to do your own thing. You've got to play as good as you can,' said Els. 'You have one chance to shoot something really decent. You've got to hope for the best on the South.'
Tiger Woods, a two-time winner and No. 2 in the rankings, shot a 3-under 69 and is part of a group tied for 35th. Woods was pleased with the round considering he has lost seven pounds recently due to illness.
'Today was a day that I got a lot out of my round because I probably should not have got what I shot,' said Woods. 'I didn't feel like I was very strong out there, but, you know, hey, I hung in there and made a few putts and lo and behold, I shot a round under par.'
Vijay Singh, last week's winner at the Sony Open in Hawaii, missed one cut last year and it was at Torrey Pines. He played better on Thursday with a 1-under 71, but the top player in the game shares 64th place.
Mickelson, who has won three times at the Buick Invitational, only managed an even-par 72. He stands in a tie for 89th place.
All of the top players were upstaged on Thursday by the 45-year-old Lehman, who was named United States Ryder Cup captain late in 2004.
Lehman flew out of the gate on Thursday with a birdie at the first when his 6-iron approach stopped less than 2 feet from the hole. He added another birdie at four after he rolled in a 6-footer, but problems arose for the 1996 British Open champion.
Lehman airmailed the green with his approach at the fifth and made bogey. He reclaimed the lost stroke with a tap-in birdie at seven, then closed his front nine with a short birdie putt at the par-5 ninth.
The five-time winner on tour parred the 10th, but hit a 7-iron to 12 feet to set up birdie at the 11th. Lehman tallied his final par of the round at 12, then sank a 30-footer for birdie at 13.
Lehman two-putted for birdie from 50 feet at the par-5 14th. He hit a pair of sand-wedges to 10 feet to set up birdies at 16 and 17. Lehman played a 6-iron to four feet for his fifth birdie in a row, then polished off a back-nine 29 with an 8-foot birdie putt at the last.
'I'm driving it long and I'm driving it in the fairway quite a bit and rolling the ball fairly well and making some putts,' said Lehman. 'I got the North Course today, which is quite a bit easier than the South, so it's quite a bit easier to get a good score on that course.'
Although it is too early to think about being a playing captain in next year's Ryder Cup, Lehman is playing spectacular golf in the last five months. Since last year's Canadian Open in September, Lehman has finished outside the top-10 only once, the 2004 Texas Open, where he tied for 17th.
'I've been focused since last August or early September,' said Lehman, who tied for ninth last week in Hawaii. 'The things I've been working on with my short game just kind of clicked. Everybody is going to miss greens and make a mistake; that when you can save yourself, make a putt for par, it keeps the momentum going. That's what all the great players have done; they have always recovered well from their mistakes.'
Wilson was flawless on Thursday with nine birdies, including a left-to-right 25-footer at 18. He is best known for being one of Annika Sorenstam's playing partners at the Colonial two years ago, but the Hawaii native wants to make a name for himself.
'The last time I was in the media room was probably with Colonial and Annika before we even teed off on the Tuesday morning,' said Wilson. 'Near the top is always exciting to get off to a good start.'
Tom Pernice, Jr. and Dudley Hart joined Els in a tie for fourth at minus-7.
Aaron Baddeley, Carl Pettersson, Pat Perez, Jason Bohn, Darron Stiles and Charles Warren are tied for seventh place at 6-under-par 66.
Defending champion John Daly, whose win last year snapped a winless streak dating back to the 1995 British Open, shot an even-par 72 on Thursday.