Phil Mickelson pursued his 60-year career with a four-year-old under 68, and was three times clear towards the end of the second day of Desert Classic in California.
The 48-year-old, who was leading overnight after his 10 birdies and an eagle in La Quinta, had a double bogey in the second round of the Nicklaus Tournament Course.
But he put down four of the last five holes for a half total of 16.
Also on the Nicklaus course world star Justin Rose shot a second 68 and eight shots back.
Russell Knox had seven birdies in La Quinta to reach five, but the Scot Martin Laird is one behind after completing two double bogeys to return a 75 after opening 65.
On Saturday, Mickelson and Rose play the third venue, the Stadium Course, where the final round of Sunday takes place.
Mickelson started his round on the 10th and hunted his second and third holes.
The double bogey came at his ninth hole, but ended in style with a superbly controlled pitch, which last turned five feet for his sixth birdie of the day.
The American was asked to compare his second round with the 60.
During his round, the left-hander was about to take a drop from the old shoulder height with the long-established method, but an officer of the rules was present to remind him that he should not be taken from the knee from January 1 onwards punishment
The last time Mickelson held the halftime of a tournament was at the 2016 Open, when he finished second to Henrik Stenson.
"It was fun, if not surprising, start for me and it's fun to get into the mix," he added.