Bill Haas set the early pace at the Phoenix Open, where he earned a two-stroke lead following the first round, while former world number one Jordan Spieth opened with a 72.
A six-time PGA Tour champion, Haas carded a seven-under-par 64 at TPC Scottsdale in Arizona on Thursday.
The 35-year-old American was flawless throughout, not dropping a shot as he posted an eagle and five birdies.
Rickie Fowler - who lost a play-off at the tournament in 2016 - is tied for second alongside Billy Horschel, Bryson DeChambeau, Chesson Hadley and Chris Kirk.
Coming off a missed cut at the Farmers Insurance Open, Fowler made a bright start on Thursday, shooting a 66, which included an eagle, four birdies and a bogey, to take a brief share of the lead.
World number two and Spaniard Jon Rahm is a stroke further back at four under following his opening-round 67.
It was a mixed bag for Rahm, who had an eagle and three birdies to go with a solitary bogey.
Bubba Watson is also three shots off the pace, while reigning PGA Tour Rookie of the Year Xander Schauffele recorded a 68.
US PGA Championship winner Justin Thomas had a double-bogey and bogey from his final three holes to finish three under alongside Schauffele.
Two-time defending champion Hideki Matsuyama posted a two-under-par 69 to start his bid for a three-peat.
As for Spieth, the American star ended the day one over and eight shots behind Haas.
Spieth - winner of three majors - holed four bogeys to go with three birdies as he struggled for consistency on day one of the event.