Dustin Johnson carded 10 birdies as he surged into a one-shot lead following the opening round of the AT&T Pebble Beach National Pro-Am.
Johnson had two bogeys in his round, which featured five successive birdies on the incoming nine, as he finished on eight under par, with JB Holmes and KJ Choi tied for second on seven-under.
Ireland's Padraig Harrington shot a 69 to finish on three-under.
Charley Hoffman was alone in fourth on six-under, with David Duval, Mike Weir and Vijay Singh among 12 players three shots off the pace on five-under.
Defending champion Johnson, playing on the Pebble Beach course and seeking his third PGA Tour win, opened with a birdie three and added a further birdie on the par-four fourth.
The 25-year-old dropped shots on the fifth and eighth, only to reclaim them at the seventh and ninth, while adding a fifth birdie of the round at the 11th.
Johnson finished with a flourish, carding birdies at the closing five holes to equal the tournament record of 30 on the back nine in his round of 64.
Holmes, beginning on the back nine at Pebble Beach, shot seven birdies and an eagle against two bogeys in his round of 65, while Choi's round was blemish free, with an eagle and five birdies.
The top three on the leaderboard all played at Pebble Beach, while Hoffman's round of 64 - featuring five birdies, an eagle and a bogey - came at Monterey Peninsula.
Duval was among three players at Spyglass Hill who recorded rounds of 67.