Fresh off last weekend's victory, under 66 to take the lead at the suspended Northern Trust Open.
First-round play was halted due to darkness, though the delay was caused earlier Thursday. Problematic winds extended morning rounds, forcing the tournament to delay tee times for the afternoon wave by about half an hour. The remaining 30 players will return to the course when play resumes at 10 a.m. (et) Friday.
Mickelson, a two-time champion at this event, birdied his last at Riviera Country Club to go to the top of the leaderboard alone. He is coming off a win at the Pebble Beach National Pro-Am, which he claimed by firing an eight-under 64 during the final round, while paired with Tiger Woods.
He is one shot ahead of J.B. Holmes and Hunter Mahan, who both fired 67s on Thursday.
Holmes is off to his best start since undergoing brain surgery in September. The procedure helped relieve symptoms of Chiari malformations, which caused him to have vertigo-like experiences.
In three previous tournaments this year, Holmes was cut twice and finished in a tie for 45th.
"It's nice to get back out here and start hitting some shots like I used to, so it's nice to put a good competitive round in on tough condition," Holmes said. "It's just nice to be back out here, and it's always encouraging when you can play good starting off on the first round."
Jonathan Byrd and Carl Pettersson carded 68s and are tied for fourth, while Sergio Garcia and K.J. Choi are among a group tied for sixth at two-under. Troy Matteson and Rory Sabbatini are also in that group, but have yet to finish their first rounds.
Many players in the morning wave struggled with difficult wind conditions, but players started dipping deeper into low numbers later in the afternoon.
Among them was Mickelson, who birdied the first and fourth to go to two-under. He caught fire around the turn, sinking birdies at the 10th, 11th and 13th. He dropped a shot with a bogey at the par-three 16th, but finished his round on a positive note.
While Mickelson hit his drive into the right rough, he placed his second 35 feet from the hole and chipped in for birdie.
"It feels really good to get that one extra shot because I felt like I left one or two out on 16, 17, and you hate to have such a good round and let a few slide late," Mickelson said. "To make that shot unexpectedly on 18 felt like I got one of those back."
That put him a shot in front of Holmes and Mahan, who wasn't much of a factor until making a late run. He started from the 10th tee and mixed three birdies, a double-bogey and a bogey in his first nine holes. However, four birdies in his final five holes allowed him to earn a share of second.
Holmes was just the opposite, getting off to a great start -- four birdies in his first five holes, while starting from the 10th. He birdied the first, but consecutive bogeys at four and five started a roller-coaster conclusion to his round.
Following those, he birdied six and seven before carding a double-bogey at the eighth. He managed a birdie at nine to go into the clubhouse with a 67.
World No. 1 Luke Donald is making his PGA Tour season debut this week, and began his tournament with a one-under 70. The Englishman -- who won four times last year while taking PGA and European Tour Player of the Year honors -- posted two birdies and a bogey.
NOTES: Defending champion Aaron Baddeley opened with a 73...Fred Couples is making a record 30th appearance at this tournament, which he has won twice (1990, '92)...Holmes has performed well at this event, finishing in the top-12 in each of the last four years...Mickelson won this event in 2008 and '09...Amateurs Patrick Cantlay and Jordan Spieth are playing this week on sponsor's exemptions. Cantlay, the No. 1 ranked amateur in the world, finished with a seven-over 78, while Spieth carded a 76.