Roberto Castro and James Hahn continued to set the pace at the Humana Challenge as they remained in a share of the lead after the second round in California.
Both added five-under 67s to their opening 63s to reach 14 under par in the pro-am event played over three courses at the La Quinta resort.
Castro looked poised to claim the outright lead at the halfway stage as he rolled in seven birdie putts at the Palmer Private course to hit the top on 16 under.
But he dropped his first shots of the week at the seventh and ninth to slip into a tie for the lead with Hahn, who was only one under for the day at La Quinta after 12 before going birdie-eagle-birdie.
Scott Stallings is just a shot behind after returning a flawless 65 which included a run of four straight birdies from the fourth, and he added three in five holes around the turn.
Stallings parred in to remain in a share of second with Darron Stiles, who birdied five of the last eight holes in his 65 at La Quinta.
Former Masters champion Zach Johnson is one further adrift after he carded three birdies and an eagle in his last six holes to hand in a second straight 66.
Man-of-the-moment Russell Henley birdied two of the last three holes to salvage a 69 and get back to 11 under, while Phil Mickelson returned an encouraging 67 at the Nicklaus Private.
But the left-hander still faces a battle to survive the 54-hole cut, as his five under score was good enough only for a share of 91st place.