Mark Wilson shot a superb 10-under par 62 to move into a share of the lead at the halfway stage of the Humana Challenge.
The 37-year-old kicked off his challenge with a 66 and backed that up with an even better round to join compatriots Ben Crane and David Toms at the top of the leaderboard on 16-under par after 36 holes at the California venue.
His round included eight birdies and an eagle but was not the lowest round of the day as Ryan Moore carded an 11-under 61 to move into a tie for 14th after going round in even par on Thursday.
Camilo Villegas was the joint first-round leader with Toms but, on a day when benign conditions produced a number of especially low rounds, the Colombian's four-under par 68 was only good enough to leave him in a tie for fourth on -13.
US stars Harris English, Chris Kirk and Bobby Gates share that score after rounds of 62, 63 and 63 receptively and, with no cut and two rounds to go, it is impossible to pick a winner at this stage with several players capable of making a run over the remaining 36 holes.
Toms carded a seven-under par 65 to keep pace with the leaders, while Crane's nine-under 63 moved him up six places into joint-first place.
Toms had not won a PGA Tour event for five years until he took the Crowne Plaza Invitational at Colonial in 2011, and the 44-year-old admitted that he had not expected to be so high up the leaderboard this week.
"It's a bit of a surprise," he said. "Coming into the week my confidence wasn't really high. I didn't play that well over in Hawaii, either tournament, but you never know. It's the type of game that it is.
It's a good start.
I'm right in a good position and hopefully I can shoot another low round tomorrow to have a chance on Sunday."
England's Gary Christian had never played in a PGA Tour event until this year but the 40-year-old is in good shape with a 68 backing up his opening 66 and he lies in a tie for 23rd on -10, while compatriot Brian Davis has it all to do after an even par round left him on two-under and with 14 shots to make up to the leaders.
Scotland's Martin Laird, tipped by many to make the European Ryder Cup team this year, is on nine-under par after a 69, while Phil Mickelson, on his season debut, could only manage a 69 and, on one-under par, has little chance of making an impact over the weekend.