In his first round of the year, the American, 48, shot 10 birdies and an eagle at La Quinta to lead by three strokes after a round delayed by fog.

England's Justin Rose is four under and Scotland's Martin Laird is seven under.

"I didn't think this was going to be a day I would go low," said Mickelson. "I came with low expectations."

"I haven't had a lot of time to practise and prepare but sometimes you have days where it clicks and the bad shots I hit I got away with."

The left-hander later tweeted: "The rust came off pretty quick and easy. Nailed it. Look out 2019!"

Rose, the world number one, carded his 68 on the La Quinta course, while Laired fired his 72 on the Nicklaus Tournament Course.

The tournament is played over three venues - La Quinta, the Nicklaus Tournament Course and the host Stadium Course, which will stage Sunday's final round.

Mickelson, who has twice carded 11-under rounds of 60 at the Phoenix Open, was eight under after 11 holes.

He found a bunker at the par-three 12th and needed a magnificent escape to six inches to save par, and chipped in for a birdie on the par-four 14th.

Needing to birdie the final two holes for a 59, he saw a birdie putt at the 17th slide by, before holing from 10 feet for a birdie at the last.

Mickelson leads by three from compatriot Adam Long, with Australia's Curtis Luck third on eight under.