South Korean Yang Yong-eun birdied six of his last nine holes to surge into a share of the lead in the Phoenix Open first round while Phil Mickelson launched his title defence with a level-par 71 in Scottsdale, Arizona.
Yang, who became Asia's first male major winner with his victory at the 2009 PGA Championship where he overhauled Tiger Woods in the final round, mixed eight birdies with a lone bogey to fire a seven-under-par 64 in dazzling desert sunshine.
The 42-year-old Korean, a double winner on the PGA Tour, took advantage of ideal scoring conditions at the TPC Scottsdale and signed off with a superb approach to three feet at the par-four last before he sank the birdie putt.
Yang, who has not recorded a single top-10 on the US circuit since he tied for sixth at The Barclays in 2011, was delighted with his up-tick in form.
"I have been playing like 'you-know-what' for a long time now," the Korean told PGATour.com through an interpreter. "I have been adjusting my swing for a long time ... and I think it's finally paying off. I missed some good chances on the front nine so I was a little bit angry with myself but I've been playing some solid golf for the last four-and-a-half rounds so I think it's good."
Yang's lead held up for most of the day until he was joined at the top by 2012 Masters champion Bubba Watson, who birdied four of his last six holes for a matching 64.
Americans Pat Perez, Kevin Stadler, William McGirt, Harris English and Chris Kirk, along with Australians Greg Chalmers and Matt Jones, were a further stroke back after opening 65s.