Hudson Swafford posted a second straight 65 to grab a one-stroke lead at the halfway stage of the CareerBuilder Challenge in California.
The 29-year-old located 16 greens in regulation, en route to making birdies on three of the four par-five holes over the Nicklaus Course in Palm Springs.
Teeing-up in his 93rd PGA Tour event, Swafford's previous highest finish is eighth, so he looks well placed to register a personal best over the weekend.
Born in Florida, the world No 204 also started well last week in Hawaii when he finished in a tie-for-13th after completing the opening 36 holes in 130 strokes.
After taking the lead on Friday, Swafford said: "I was very solid, very patient. Hit a lot of good quality iron shots, hit a lot of good putts, gave myself a lot of chances.
"Just really focusing on rhythm with everything I do. It's really kind of coming together.
"I haven't been in a bad position off the tee, which is really key, and the putter feels good in my hands."
His nearest challengers are New Zealand's Danny Lee and American rookie Dominic Bozzelli, who had led after round one.
Both teed-off at La Qunita Country Club, with Dominic Bozzelli carding a second round 67 while Lee fashioned a joint best-of-day 64.
Englishman Greg Owen is four strokes off the pace, following a brace of 67, and is tied-for-sixth alongside Scotsman Martin Laird and five-time major winner Phil Mickelson.
Laird fired 66 over the Stadium Course, with Mickelson hitting an identical score over Nicklaus.
The 46-year-old American is playing in his first event since October, following surgery on a hernia, with Friday's round including an eagle-three at the par-five 11th and also a birdie from a greenside bunker at the first hole - his 10th of the day.
On a rare wet and cold day in the California desert, Mickelson admitted: "I feel like I'm improving quite a lot from when I started practicing last Saturday.
"I'm hitting more and more good shots each day and fewer bad ones."