Andrew Landry and Scottie Scheffler ended the third round tied for the lead at The American Express.
Landry and countryman Scheffler are four strokes clear atop the leaderboard after Saturday's penultimate round.
A one-time winner on the PGA Tour, Landry climbed two positions thanks to his seven-under-par 65 in California.
Landry – playing the Nicklaus Tournament Course at PGA West – made a red-hot start with six birdies from his opening nine holes, including four in a row from the 14th.
Scheffler, who was tied for the 36-hole lead alongside Rickie Fowler, stayed top thanks to his six-under-par 66.
On the Stadium Course, Scheffler was bogey-free with six birdies throughout day three.
American star Fowler dropped down to third following his two-under-par 70, which included four birdies and two bogeys.
Ryan Moore (67) and Chase Seiffert (67) are a stroke further back at 16 under through 54 holes, a shot ahead of Andrew Putnam (65), Abraham Ancer (66) and Sebastian Cappelen (64).