Five-time major champion Phil Mickelson carded a six-under 65 to share second place after the opening round of the AT&T Pebble Beach Pro-Am in California.
The 48-year-old world number 29 made five birdies on the back nine at Monterey Peninsula's Shore course.
Jason Day also shot a 65 but world number 155 Brian Gay and 285th-ranked Scott Langley shot 64s.
Northern Irishman Graeme McDowell is four under after bogeying the final hole at Pebble Beach.
Mickelson, who was runner-up to Adam Long at last month's Desert Classic but missed the cut at the Phoenix Open last week, hit all 13 fairways for the first time in a PGA Tour round since the Farmers Insurance Open in 1998.
Englishman Tommy Fleetwood, the world number 14, ran up a triple-bogey seven at the 13th en route to a 73 at Monterey.
Compatriot Paul Casey birdied the final two holes at Pebble Beach to return a three-under opening round.
The players each play at Pebble Beach, Monterey and Spyglass Hill over the first three days before the final round at Pebble on Sunday.