Jeff Maggert posted a 7-under-par 63 to share second place with John Senden and Woody Austin. Four more players -- Nick Watney, David Hearn, Phillip Price and Ted Purdy -- are one stroke further back at minus-6.
Gamez, a two-time winner on the PGA Tour, got off to a quick start with a birdie on the first. At the fourth, He hit his approach shot within 10 feet and ran home that putt for his second birdie.
The 37-year-old dropped a wedge within 12 feet at the seventh and made that for birdie. Gamez drained a long birdie putt on No. 8 to get to 4 under, then kept going as he chipped in for birdie on the ninth of the Resort Course at LaCantera Golf Club.
'I chipped in on No. 9,' Gamez said. 'I hit a poor iron shot to the right and chipped it in for birdie. That kind of kept my round going. Stuff like that is nice to keep a round going.'
Gamez sank a 30-foot birdie try on the 11th to move to minus-6. He then dropped in birdie putts on 14 and 16 to get to eight-under.
'It was a lot of fun. I played pretty well,' said a modest Gamez. 'I missed a couple there at the end, but made a couple good putts as well in the middle of the round. I made a couple good par saves that kind of saved my round there.'
Maggert started on the back nine. He birdied the 10th, but stumbled to his only bogey at the next. He dropped in consecutive birdie putts from the 13th.
After a birdie on No. 18, Maggert turned it on around the turn. The 41-year- old rolled in birdie putts on the second and fourth. After a pair of pars, Maggert closed with birdies on seven and nine to share second place.
Senden played his first six holes 1 under with a birdie on the second. He got hot with birdies on seven and nine to turn at minus-3. The Australian picked up another birdie on the 11th.
The 34-year-old eagled the par-5 14th, then he birdied the last to end at minus-7.
Austin began on the second nine and got off to a fast start, as he holed out for eagle on the par-4 11th. He then birdied the 12th and 14th to move to 4 under.
The 41-year-old birdied No. 18. Around the turn, Austin climbed to 6 under with a birdie on the par-4 fourth. He stumbled to a bogey at the next, but closed with birdies on seven and nine to share second place.
Defending champion Bart Bryant opened with a 5-under-par 65. He shares ninth place with Harrison Frazar, Bob Heintz, Brendan Jones, Brad Lardon, Larry Mize, John E. Morgan, Rod Pampling, Aaron Baddeley, Olin Browne and Mark Wilson.