The 25-year-old from New York state broke clear of a tightly-bunched leaderboard by sinking a 14-foot birdie putt on his final hole, the par-four ninth, to cap a bogey-free day in the California desert.
Venezuelan Vegas and Americans Harold Varner III, Patton Kizzire and Hudson Swafford opened with 65s while fan favourite Mickelson, competing for the first time since recovering from a pair of offseason surgeries, carded a 68.
"That jump-started it (my round) for sure," Bozzelli told Golf Channel about the eagle on his fifth hole of the day. "I made two big par saves today too. On 15, I got up and down from 85 yards and the other one was on two ... made a 12-footer to save par.
"Those were huge momentum boosts to keep the round going. I was able to make some putts coming in and (get) off to a good start.
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“I've been working hard, doing all the right things on and off the course, training hard, so it was nice to see it pay off a little bit.”
Mickelson, who had surgeries for a sports hernia last October and December, was delighted to mark his return to competition with five birdies and a lone bogey, despite feeling a little rusty with his game.
"I thought it was phenomenal,” said the 46-year-old American. “I struck it horrible but I scored like out of my mind so I am very happy with it.”
(Reporting by Mark Lamport-Stokes in St. Augustine, Florida; Editing by Frank Pingue)
