Mathis ahead in Connecticut
David Mathis claimed the lead on six under after 12 holes on day one of the Travelers Championship in Cromwell, Connecticut.
The American birdied five holes and eagled and bogeyed once to take a one-shot lead over four players.
Australian Nathan Green and Will Claxton of the United States had finished their round, both carding 65 at the TPC River Highlands, while the USA's Roland Thatcher and Sweden's Fredrik Jacobson were on course to card the same score after 11 and 10 holes respectively.
It was Mathis who topped the leaderboard, however, and he came firing out of the traps.
The 38-year-old, who was cut at this year's US Open in his only major appearance to date, birdied the 10th - his first hole - eagled the 11th and picked up shots on three of his next four holes.
Although he bogeyed the 18th, he birdied the par-four third to take the outright lead.
England's Gary Christian finished on four under along with American Jerry Kelly, while Masters winner Bubba Watson was a shot further back on three under at the turn.
Ian Poulter and recently-crowned US Open champion Webb Simpson both carded a two-under-par 68, with Irishman Padraig Harrington and winner of the 2010 Open Louis Oosthuizen among several players on one under.
Patrick Cantlay shot the lowest round in PGA Tour history by an amateur when he shot a course-record 60 here last year but he carded a five-over-par 75 today.