The 38-year-old Mathis, who missed the cut last week in the U.S. Open, began play on the back nine, making a birdie on 10 before holing out from 158 yards shot on the par-3 11th hole. He was 6-under after six holes.
Nathan Green, former Swainsboro, Ga., resident Will Claxton and defending champion Fredrik Jacobson shot 65 on a day that saw temperatures soar into the 90s.
U.S. Open champion Webb Simpson and Masters Tournament winner Bubba Watson played together and finished in a group of 10 at 66. The third member of the threesome, PGA champion Keegan Bradley, shot 68.
“We were relaxed all day,” Simpson said. “Bubba is my Presidents Cup partner. We always laugh together. And I’ve played a lot of golf with Keegan this year. He’s a good friend. We had a lot of fun feeding off each other, and luckily, we all played well.”
Mathis’ ace was the shot of the day. He said he was just trying to cut a 9-iron close to the pin and it hit exactly where he aimed, bounced right and into the hole.
“It was an awesome start,” he said. “I was hitting a lot of great shots (later), and I guess it felt like a lull compared to how I started.”
Green teed off at 6:50 a.m., well before heat and humidity set in, setting the early mark with 65. Claxton opened his round with a birdie and an eagle, but finished with a bogey on 18.
“To start out birdie-eagle, that’s huge,” Claxton said. “I obviously had the driver going. I drove the ball well today. It wasn’t as difficult as I thought it might be.”
Jacobson, who picked up his only PGA Tour win at the event a year ago, spent much of the day atop the leaderboard before a double bogey on 16 dropped him into a three-way tie for second.
“I knew it was going to be challenging in this heat, and if you start to miss a few shots, it can get to you,” he said. “So I was just happy to get through this day.”
One of Jacobson’s playing partners, former Masters champion Zach Johnson, also had a tough finish. He was 3-under when he hit a drive over the green at 15. He made a six there and a seven on the par-4 17th, where he tried to putt from the fringe, and needed three more after making it to the green.
A gallery of fans five and six deep greeted Simpson, Watson, and Bradley on the first tee, and many followed them throughout what all three said was a relaxed round.
“Any time you can play with those guys, it’s fun,” Watson said. “We learn from each other. We watch each other. We’re making some jokes out there. We were having a good time. It was good.”
But it wasn’t fun for everybody. Former UCLA star Patrick Cantlay made his pro debut with 75 on the same course where he made headlines last year with a second-round 60 as an amateur.
“I started off poorly with a couple of doubles and couple weird things happened, and it just added up to a bad round,” Cantlay said.