Robert Karlsson holds a share of second place after David Mathis shot an opening round 65 to take a one stroke lead in the FedEx St Jude Classic in Memphis, Tennessee on a steady day for World Number Two Lee Westwood.
Mathis birdied three of the first five holes on the front nine to get off to a flying start, before making bogey on the par three eighth.
The 37 year old also picked up three more shots on the back nine to finish top of the leaderboard on five under.
Westwood was one under for the day after losing a shot on the third hole before putting together a run of three birdies in four holes on the back nine.
Five players were tied for a share of second after rounds of 66.
Sweden's Karlsson was the only non-American among the group, which included John Merrick, Kris Blanks, Kevin Kisner and Colt Knost.
Merrick hit four of his five birdies in a purple patch between the 13th and 17th holes, while Blanks had two bogeys to weigh against six birdies.
Keegan Bradley and Argentina's Fabian Gomez were next on three under, while a pack of ten were one shot back.
