Englishman Greg Owen, ranked 342nd in the world, carded a bogey-free six-under 64 for a share of the lead.

The 43-year-old has never tasted victory on the PGA Tour in 213 attempts since 1999, while his only success on the European equivalent came 12 years ago at the British Masters.

But after starting on the back nine, he made five birdies in six holes, including four in a row, from the 16th to soar to the top of the leaderboard - having already picked up a shot at the 12th - alongside American pair Brooks Koepka and Ryan Palmer.

Despite an excellent start to his campaign, Owen was refusing to get carried away about his chances as he told the PGA Tour's official website: "There's a long way to go. There are so many top-class guys here, you can't even think like that."

Owen's previous highest finish in Memphis came three years ago when he finished in a tie for 11th, while he was in a share for 60th last year and has also missed the cut twice.

"I don't look at past results," he said. "It means nothing. To finally hit the shots I want to hit, I just want to keep hitting them. Wherever it leads us, it leads us."

Asked if he could remember the last time he topped a leaderboard, Owen, who turned professional in 1992, added: "I don't remember. I don't look at stats."

Palmer had similar fortunes to Owen, making four birdies on the back nine before carding two on the front in a bogey-free round, while Koepka's could not have been more different.

After making two birdies on the back nine, the Floridian carded another six after the turn as well as bogeys at the second and seventh.

England's Brian Davis is alongside three other players in a tie for fourth after his 65, with the world number 266 making birdies at the second, third, ninth, 10th and 17th holes. America's Scott Brown, New Zealand's Steven Alker and Richard Sterne are also on five under.

Defending champion Ben Crane, who beat Troy Merritt by one stroke last year, is among those a shot further back after making three bogeys in his final five holes.

The five-time PGA Tour winner, starting on the back nine, appeared set to go clear at the top after five successive birdies from the 18th left him on seven under after 13 holes but he dropped shots at the fifth, seventh and ninth holes to sit two adrift of the pace-setters.

Phil Mickelson is on two under, alongside Scotland's Martin Laird, while former world number one Luke Donald, who on Monday qualified for next week's US Open, carded a one-under 69.