Cromwell - David Mathis hoped to start strong at the Travelers Championship after missing the cut last week in the U.S. Open.

The 38-year-old Mathis birdied his first hole, then holed out from 158 yards on the par-3 11th hole. He knocked in a 49-foot birdie putt on his third, was at 6-under par after six holes, and fished with a 6-under 64 for a one-shot lead.

"It was an awesome start," said Mathis, who has never finished better than eighth in a PGA Tour event. "I was hitting a lot of great shots (later), and I guess it felt like a lull compared to how I started."

Nathan Green, Will Claxton and defending champion Fredrik Jacobson shot 65 on a day that saw temperatures soar into the upper 90s.

U.S. Open champion Webb Simpson and Masters 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 a 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 nine iron close to the pin and hit it exactly where he aimed.

"It kind of bounced and stumbled right and went right in the hole," he said.

Green teed off at 6:50 a.m., well before heat and humidity set in, setting the early mark with a 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 to 5 under and into a three-way tie for second.

One of Jacobson's playing partner's, 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 6 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."