Putnam covered his back nine in a sizzling seven-under 29 to finish a picture-perfect day a stroke in front of compatriots Blake Adams, John Peterson, Scott Pinckney and 2012 champion Mark Wilson, and Italian Francesco Molinari.
Holder Patrick Reed, who won the Hyundai Tournament of Champions in Hawaii 10 days ago, launched his title defence with a 65 while twice former winner Phil Mickelson, playing his first competitive round since late September, carded a 71.
"It was like a light switch," Putnam told Golf Channel about the transformation in his game from the seventh hole onwards. "I said I needed to make some birdies, so I did.
"I played decently solid before that, just made a few mistakes to make bogeys, but I just lit it up coming in."
Putnam, a three-times champion on the lower-tier Web.com Tour who has never finished better than fourth in a PGA Tour event, was not planning to dwell on his opening round for long.
"You've kind of got to forget about it because we are playing a totally different golf course tomorrow ... so kind of put that out of my memory and now I am focused on the Palmer (course) for tomorrow," he said.
"There were a lot of low scores shooting out there too so you've still got to make birdies because 25, 27 under (par) wins this thing."
Five-times major winner Mickelson, who has not played competitively since the United States lost to Europe at the Ryder Cup, mixed four birdies with three bogeys at La Quinta Country Club.
"Even though this feels like the worst day I've had in months, I am excited about my game and getting back out tomorrow," the left-hander said after tootling 31 putts.
"I feel like I played a little bit tight today, kind of steered it a little bit. I'll loosen up and hopefully the way I am playing will show in the score. Today it just didn't."
(Reporting by Mark Lamport-Stokes in Los Angeles; Editing by Frank Pingue)
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