Patrick Cantlay secured a one-shot lead on 14-under par ahead of Tom Hoge on the second day of the American Express in California on Friday.
The world number four followed up his impressive round of 62 on the opening day with a four-under 68 to hold the outright lead at the end of day two, with Hoge following up a first day 65 with another respectable round of 66 to sit on 13-under.
The best round of the day came from Will Zalatoris, who shot an 11-under 61 to move up 93 places to joint-third after having hit just 10 greens in his opening round 71.
The 25-year-old American managed 12 birdies, including each of his last seven holes to climb up the leaderboard, and now sits level on 12-under with fellow countrymen Lanto Griffin, Greyson Sigg, Cameron Young and Joseph Bramlett.
His drive on the final hole actually ended in the rough on the adjacent first hole, but he was still able to make birdie.
“I think today I just gave myself chances," Zalatoris said after his round. "I hit a lot close and made a couple 20, 30 footers to keep the round going and obviously... making birdie on nine from the wrong fairway is kind of the icing on the cake."
Sam Ryder, Roger Sloan, Zach Johnson and Paul Barjon ended their second rounds tied for eighth on 11-under.
Meanwhile, Lee Hodges, who held the lead with Cantlay at the start of day two, could only muster an even-round of 72 and now finds himself tied for twelfth with 11 other competitors.
Among them is Sahith Theegala, who shot an eagle and eight birdies as part of a round of 62 to climb 98 places to inexplicably sit alongside the previous day's overnight joint-leader.
World number one Jon Rahm was unable to build on his steady first round of 66 as he hit five birdies and three bogeys during his 70 to sit tied for 32nd on eight-under.