World No 1 Scottie Scheffler and 18-year-old Blades Brown are one shot off leader Si Woo Kim on a congested leaderboard after three rounds of The American Express.
Scheffler and Brown both carded four-under 68s at the tricky Stadium Course to reach 21 under par, with Kim marginally ahead after a six-under 66 at La Quinta Country Club.
Brown, a day after narrowly missing out on a 59 at the PGA Tour event, birdied his final three holes on Saturday, including from 17 feet at 17 and 45 feet at the last.
He also found time to play rock-paper-scissors with a young fan and is seemingly unfazed by the fact he could become the youngest winner in nearly a century, if not longer.
Charles Kocsis won the Michigan Open in 1931 at 18 years and six months - a couple of months younger than Brown - but that tournament was regarded as a regional event.
Tom Morris won his first British Open in 1868 at age 17.
Brown said: "I'm 18 years old playing on the PGA Tour. How awesome is that? I finished high school about two weeks ago, so it's nice to have that burden off my back. I'm looking forward to Sunday."
Scheffler, playing his first event of the season, notched six birdies and two bogeys as he played in windy conditions, with a 25-foot par save at the last keeping him right on Kim's tail.
Eric Cole and Wyndham Clark are two back at 20 under, with Tom Hoge, Matt McCarty, and Andrew Putnam at 19 under.
Sweden's Ludvig Ã…berg withdrew with illness on Saturday.
Watch round four of The American Express live on Your Site Golf from 4.30pm on Sunday. .
