LA QUINTA, Calif. -- Phil Mickelson still feels as young as ever. He still plays that way, too.
Mickelson began his 27th full season as a pro Thursday by flirting with one of the few feats he hasn't accomplished — golf's magic number. The 48-year-old left-hander still shot a 12-under 60 in the Desert Classic, tying his career-low score he last shot in the Phoenix Open six years ago. It was the most under par he has been in any of the 2,077 rounds he has played on the PGA Tour.
"It was a kind of a lucky day for me in the sense that I did not feel sharp heading in," Mickelson said. "I haven't really had the intense practice sessions that I would like, but I felt like all parts were OK and it just clicked. Some days you have those days where it just clicked. And the bad shots that I hit, I got away with. I was able to kind of not have the big score."
Needing to play the final two holes in 2 under to shoot 59 on the foggy, rainy day at La Quinta Country Club, Mickelson missed a 15-foot birdie try on the par-4 17th before holing a 9-footer for birdie on the par-4 18th.
The Desert Classic is the only PGA Tour event to yield two sub-60 rounds. David Duval had a 59 at PGA West's Palmer Course when he won in 1999. Adam Hadwin shot 59 at La Quinta in 2017.
"I was aware of it," Mickelson said. "I was giving it all I had and I had a good chance. On 17, I hit a nice tee shot in a good spot to kind of hook a sand wedge into that back right pin for me. And I hit a good shot, I had 18 feet though, I should have hit that closer, but still had a good chance to make the putt. Made a good birdie on 18. That's not an easy hole for me, that shot the way it sits along the water."
Mickelson had a three-stroke lead over Adam Long, the 31-year-old PGA Tour rookie who finished off a 63 in the dark on PGA West's Nicklaus Tournament Course.
The fog-delayed round was Mickelson's first on tour since early October and the first in competition since beating Tiger Woods in Las Vegas in November in a made-for-TV event.
"I knew it wasn't far off, but it didn't feel like I was ready to go," Mickelson said. "I just felt like I needed to be careful. I felt I played a little bit more conservative."
Lefty birdied the first two holes and played the back-to-back par 5s in 3 under with a birdie on No. 5 and a 5-foot eagle putt on No. 6. He added a birdie on the par-4 ninth for a front-nine 30, and birdied the par-4 10th , par-5 11th, par-5 13th and par-4 14th, holing a chip from in front of the 14th green.
"That was an interesting shot because I could have easily lost one and I ended up picking one up," he said.
He then ran in a 5-footer for birdie on the par-4 16th.
The tournament winner in 2002 and 2004, Mickelson will play the Nicklaus Course on Friday and PGA West's adjacent Stadium Course — also the site of the final round — on Saturday. He won the World Golf Championships-Mexico Championship last year for his 43rd PGA Tour title and first since the 2013 British Open.
Long eagled the par-5 fourth and had seven birdies — five in a row from Nos. 9-13 — in an eight-hole stretch.
"I just kept hitting it pretty close and making some good rolls and they were going in," Long said. "I just kept feeding off it and tried to keep the pedal down."
Australia's Curtis Luck was third at 64, also playing La Quinta.
Hadwin was at 65 with Trey Mullinax, Wyndham Clark and Martin Laird. Hadwin played the Stadium Course, Mullinax and Laird opened on the Nicklaus layout, and Clark was at La Quinta.
Defending champion Jon Rahm shot a 66 at La Quinta. He's fighting a lingering flu bug.
"Still pretty weak, which is possibly why I wasn't hitting it quite as far," Rahm said. "Not fully recuperated. My body is not a hundred percent."
Top-ranked Justin Rose had a 68 at La Quinta in his first start of the year. He's the first No. 1 player to play the tournament since the world ranking began in 1986.
"It's kind of like you're at the starting line and they kept dragging it back 30 minutes with the fog," Rose said. "So, that was tricky just to keep warm really and keep loose. But once I got going I felt like I played really well."