South Korea's Sungjae Im eked out a one-shot lead at The American Express after a 65 on Friday saw him at the top of a stacked leaderboard at La Quinta.
The 2019 PGA Tour Rookie of the Year followed on from his 68 to put him 11-under for the tournament, with the 22-year-old's blemish-free second round on the Stadium Course including a pair of birdies on the seventh and eighth.
Overnight leader Brandon Nagy is one of five tied for second place on ten under after he missed a chance to join the South Korean at the top with a bogey on his last hole of the day.
Also on ten under are Abraham Ancer, Tony Finau, Nick Taylor and Si Woo Kim, with three others a shot further back.
Paul Casey is the highest placed Briton after his round of 65 pushed him up to a tie for 18th on seven under, while Scotland's Russell Knox is two shots further back and tied for 37th.
Brooks Koepka, Kevin Na and Phil Mickelson were among those failing to make the cut at four under.