Ted Potter jnr. shot his second successive 67 to share the lead at the halfway stage of the Pebble Beach Pro-Am alongside Brandt Snedeker.
The 30-year-old from Florida, playing at the par-70 Monterey Peninsula course in the three-venue event, was five-under for his round after an eagle three at the 10th but gave shots back with bogeys at 14 and 15.
But he clung on to the lead until late in the day when his fellow American signed for a 68 at par-72 Spyglass Hill. Snedeker is the PGA Tour's form player and currently leads the FedEx Cup standings by 200 points.
The pair will head into Saturday's third round a shot clear of Sweden's Freddie Jacobson and Americans John Merrick, Patrick Reed and Hunter Mahan.
Potter is chasing his second PGA Tour victory after winning the Greenbrier Classic in his rookie year of 2012. He is currently 64th in the FedEx Cup rankings.
Mahan had a share of the first-round lead alongside Scotland's Russell Knox but slipped back after managing just a 69 at Monterey Peninsula.
Knox fared even worse at Spyglass Hill with a 73 and is now on five-under, three shots off the pace.
England's Lee Westwood also struggled after his opening 68, carding a 70 at Monterey Peninsula that leaves him on four-under.