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 cloudy, 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.

"I was aware of it," Mickelson said about shooting 59. "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."

Phil Mickelson shot a 60 on Thursday, his lowest round in six years. Jeff Gross/Getty Images

The round was his 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 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.

Top-ranked Justin Rose, also making his 2019 debut, had a 68 at La Quinta -- one of three courses used in the event. He's the first No. 1 player to play the tournament since the world ranking began in 1986.