English pair Greg Owen and Brian Davis both enjoyed excellent opening rounds at the FedEx St Jude Classic as Dustin Johnson was forced to withdraw midway through the first day.
Owen defied the searing heat and humidity at TPC Southwind in Memphis and had a superb run of five birdies in six holes midway through his six-under 64 which earned him a share of the lead with Brooks Koepka and Ryan Palmer, who also kept a bogey off his card.
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."
The same could not be said for Koepka, who played the back-nine in two under and mixed six birdies with two bogeys in a mixed-bag of a front-nine 31 which featured only a single par.
Owen's fellow English journeyman Davis carded five birdies in a faultless opening 65, while defending champion Ben Crane raced to seven under with a remarkable run of five consecutive birdies only to drop three shots over his last five holes.
American veteran Boo Weekley also failed to capitalise on a flying start as he dropped three straight shots to slip from five under to two under before salvaging a 67 along with former US Open champion Lucas Glover.
Phil Mickelson, who will again bid to complete a career grand slam of majors at next week's US Open, covered the back nine in four under but struggled to an outward 37 to finish on two under.
Steady start for Donald
Luke Donald, fresh from coming through 36 holes of qualifying for Chambers Bay on Monday, recovered from a double bogey at the 18th with three front-nine birdies as he rescued a 69 along with two-time US Open champion Retief Goosen.
But the early headlines were created by pre-tournament favourite Johnson, who bogeyed his first three holes and then put together six pars before heading for the clubhouse.
The world No 7 complained of feeling unwell throughout the nine holes that he managed, but he allayed fears that he could be a doubt for the second major of the year.
Johnson posted a statement on his Facebook page, which read: "Thanks everyone for all your concern and support. I hated to have to withdraw this morning, but thought it was the best thing to do under the circumstances.
"Hopefully, I’ve only got a little bug, but didn’t want to make it worse by playing in the extreme heat and humidity. Special thanks to all my fans in Memphis, my friends at FedEx and of course, St. Jude Children’s Hospital. I’m sorry to disappoint, but I’ll be back!"
Northern Ireland's Graeme McDowell, the 2010 US Open champion, had a day to forget after a six-over 76. He had been looking to build some momentum ahead of the trip to Washington, but carded five bogeys, a double bogey and just one birdie to sit in a tie for 145th.