Charlie Wi leads the Pebble Beach National Pro-Am by three shots with one round remaining, ahead of Ken Duke and Tiger Woods.
South Korean Wi posted a three-under-par third round of 69 at Spyglass Hill, one of three Californian courses hosting the US$6.4 million event.
He tops the leaderboard at 15-under overall, three strokes clear of Duke.
The American, playing Monterey Peninsula, carded a five-under 65 to reach 12-under, one shot ahead of 14-time major champion Woods, who produced a five-under 67 at Pebble Beach to sit outright third at 11-under.
Woods' long-time rival Phil Mickelson is just two strokes further back, one of five players tied for fourth place at nine-under.
He is joined in the all-American logjam by Kevin Na, Dustin Johnson, Brendon Todd and Hunter Mahan.
Two more Americans, Bob Estes and Ricky Barnes, share ninth place at eight-under, alongside Ireland's Padraig Harrington.
After Wi, three-time major winner Harrington is the highest-placed non-American on the leaderboard, with Australian Aaron Baddeley a stroke further back and tied for 12th.
Duke and Woods appear best-placed to interrupt Wi's challenge for a first victory in the US.
But the 39-year-old will be tough to catch if he produces another display to match Saturday's solid showing.
Wi holed just three birdies for his round, at four, 12 and 17, but also went bogey free, demonstrating his consistency with 15 pars throughout the day.
Duke also avoided a bogey, holing five birdies and 13 pars.
Woods, meanwhile, did drop a shot at the par-three 12th, but carded six birdies to stay in contention for what would be just his second victory in over two years.