Connecticut - Charley Hoffman fired a nine-under-par 61 on Thursday to seize a one-stroke lead over fellow American Hunter Mahan after round one of the $6.1 million PGA Travelers Championship.
Hoffman, who shared 45th at last week's US Open, eagled the par-4 10th and par-5 13th holes and after a birdie at the 15th needed to birdie the last three holes to match the US PGA's all-time record low round of 59.
"It sort of crossed my mind, but not for long," Hoffman said. "I learned that 16, 17, 18 aren't an easy test."
He only managed a birdie at the 18th, but it was enough to put him atop the leaderboard by a stroke over Mahan, who shared fourth at the US Open, and two shots over 2012 Masters champion Bubba Watson.
Past major winners Zach Johnson and Webb Simpson were in a group sharing fourth on 65 that included fellow American John Merrick, Venezuela's Camilo Villegas, Canada's Graham DeLaet and Australia's Rod Pampling.
US Open winner Justin Rose of England fired a 67 to share 18th, with a high point of the day being the first time he heard his name announced as a major champion.
"Being announced as the 2013 US Open champion, I couldn't help but smile before I hit my first tee shot," Rose said. "That's an achievement that I've been dreaming about.
"I had a sluggish four or five holes where I struggled, but I stayed patient. I've stayed sort of committed to the same things that worked so well for me last week. That was my goal today, really."
Defending champion Marc Leishman of Australia opened on 66. He finished one stroke ahead of Mahan and Hoffman last year to capture the crown at the TPC River Highlands for his first US PGA victory.
Hoffman's bogey-free round included birdies at the par-5 sixth and par-4 seventh, his pair of eagles sandwiched around a birdie at the 12th and birdies on two of the last four holes.
He fired a back-nine 28, the lowest nine-hole score of his PGA career and the US tour's lowest back nine since Vijay Singh fired a 28 in 1998.
And Hoffman did it with a broken tooth, albeit one that was not causing him pain.
"The tooth broke at The Players this year. I haven't had time to go home," Hoffman said. "Got it re-plastered a couple times, so just going to get it re-glued. Nothing major, no pain or anything."
Mahan, who won this event in 2007, began on the back nine with a birdie, ran off three birdies in a row starting at the 13th and added another at 17, birdied the par-4 second and bagged two final birdies at the par-3 fifth and the sixth.
Watson opened with a pair of birdies but took a bogey at fourth and followed a birdie at six with a bogey on the next hole before closing the front nine with another birdie.
He added birdies at 11 and 13 before making an eagle at the par-4 15th and a birdie at 17.
Leading scores on Thursday after the first round of the $6.1 million US PGA Travelers Championship (par-70, USA unless noted):
61 - Charley Hoffman
62 - Hunter Mahan
63 - Bubba Watson
65 - John Merrick, Webb Simpson, Rod Pampling (AUS), Camilo Villegas (VEN), Graham DeLaet (CAN), Zach Johnson
66 - Chris Stroud, Tommy Gainey, John Huh, Padraig Harrington (IRL), Richard Lee, Patrick Reed, Marc Leishman (AUS), Chris Kirk
67 - John Rollins, Robert Streb, Dicky Pride, Bo Van Pelt, Lee Westwood (ENG), Jerry Kelly, Bryce Molder, Stewart Cink, Brendon de Jonge (ZIM), David Branshaw, Ricky Barnes, William McGirt, David Mathis, Justin Rose (ENG), Angel Cabrera (ARG), Nick O'Hern (AUS)