Scotland's Russell Knox and American Hunter Mahan are tied for the lead after the AT&T Pebble Beach National Pro-Am first round.
Knox and Mahan both shot rounds of six under on Thursday, on one of the three courses used for the PGA Tour event in California.
Knox starred on the Monterey Peninsula course, shooting eight birdies in a round of 64.
The 27-year-old hit a bogey on the first hole but quickly recovered, hitting four birdies from his next seven holes.
And he was also hot on the back nine, finishing well to claim the joint lead alongside world number 26 Mahan.
Mahan played on the Pebble Beach course and looked set for a blemish-free round until he produced a bogey on the 17th. He still hit seven birdies in a six under 66.
A group of six players are tied for third, just one shot off the pace at five under.
American pair Matt Every and Ted Potter Jr both carded rounds of 67 on Pebble Beach and Englishman Greg Owen, Japan's Ryuji Imada and American Scott Langley achieved the feat at Monterey Peninsula.
And South Korean Seung-Yul Noh is also at five under after shooting a 67 at Spyglass Hill.
World number eight Lee Westwood heads the list of nine players tied for ninth at four under, with in-form American Brandt Snedeker also among the pack.
Westwood hit five birdies in a four-under 68 on the Pebble Beach course.
Defending champion Phil Mickelson entered the event in terrific form after his win at the Phoenix Open last week.
But Mickelson was not among the leaders on day one, shooting a one under 69 at Monterey Peninsula.
Mickelson was on track for a good score before two late bogeys proved costly, finishing the day tied for 57th spot.