The 32-year-old American made the most of surprisingly soft conditions at the TPC Summerlin, firing a seven-under-par 64 to set the pace with compatriots Will MacKenzie, Michael Letzig and Cameron Tringale, plus Australian John Senden.
George McNeill, the 2007 champion, opened with a 65 to match fellow Americans Nicholas Thompson, Ryan Palmer, Vaughn Taylor and Martin Flores.
Among the bigger names competing in the penultimate event on the 2010 PGA Tour, Davis Love III and John Daly returned 66s while U.S. Ryder Cup player Hunter Mahan carded a 67.
On a cool, overcast morning in the Nevada desert, Garrigus birdied three of the first seven holes before ending the day in a five-way logjam at the top of the leaderboard.
"I've never seen the golf course this soft," the Arizona-based professional told reporters after recording eight birdies and a lone bogey. "Conditions were perfect. No wind.
"When that happens, you can go low. I ended up making a bunch of putts and shooting seven under. It was a great start."
MEMPHIS BLUES
"It's kind of nice when you have a job where you make half a million dollars and you're furious. I've got one of the greatest jobs in the world."
Garrigus described Memphis as an important stepping stone in his development as a PGA Tour player.
"I know I can win," he said. "I know I can do it. If I can just get over that mental hurdle to do it, I'm going to win a lot out here. I feel like I can."
MacKenzie is a double winner on the PGA Tour but has posted only one top-10 this season in 21 starts and needs a strong finish to the year to secure his playing privileges for 2011.
"I am feeling good," said the American who lies 146th in the money list where the top 125 earn full exemptions for next season. "I have a chance to play great but a tie for 40th (here) doesn't do anything for me at all.
"I got to have a big finish. I got to have two good finishes or one fantastic one. I'm going to try to just make as many birdies as possible. If I have to go to Q (qualifying) School, I'll go to Q School."
Britain's Martin Laird, who clinched his maiden PGA Tour victory here last year in a three-way playoff, and 2008 Masters champion Trevor Immelman of South Africa opened with 69s.
(Writing by Mark Lamport-Stokes in Los Angeles; Editing by Steve Ginsburg; To query or comment on this story email sportsfeedback@thomsonreuters.com)
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