England’s Greg Owen produced a bogey-free six-under-par 64 on Thursday to join Brooks Koepka and Ryan Palmer atop the leaderboard after one round of the PGA Tour’s St Jude Classic.

Owen and Palmer both had six birdies with no bogeys on the par-70 TPC Southwind course, while Koepka fired eight birdies with two bogeys to join the leading group in the final tune-up for next week’s US Open.

Koepka, whose strong start to the season included victory in the Phoenix Open, added this week’s tournament to his schedule in hopes of regaining momentum going into the second major of the season.

A rib injury and his own expectations after early-season success had led to a downturn.

He decided to play this week with a new approach.

“I felt like I was playing really well,” Koepka said. “I just wasn’t scoring well.

“Too many double bogeys and being a little too aggressive. To kind of pull the reins back and play a little safer, play a little less aggressive – it’s nice to see it kind of pay off.”

Palmer said putting was key to his round.

“Something about these greens gets me going,” said Palmer, a three-time winner on the US Tour.

He made all six birdies in his first 11 holes and said he wasn’t at all disappointed he couldn’t pick up any more shots in his final seven holes. More important, he said, was not giving any back.

“You can’t win it on Thursday, but you sure can lose it.”

Owen’s round included four birdies in a row from the 16th through first holes.

Still seeking his first PGA Tour win, Owen said it was too soon to start thinking about lifting the trophy on Sunday.

“There are so many top-class guys here, you can’t even think like that,” Owen said.

Among the marquee players warming up for the US Open, five-time major champion Phil Mickelson opened with a two-under-par 68.

Mickelson teed off on 10 and hit just three of seven fairways in regulation on his first nine, but needed a mere 11 putts. Coming in, he found only two of seven fairways, and required 15 putts.

“I had a couple of opportunities coming in that would have really made the round a few more shots lower, but they didn’t quite fall,” said Mickelson, who finished with four birdies and two bogeys. “That happens.”

American Scott Brown, New Zealand’s Steven Alker, England’s Brian Davis and South African Richard Sterne share fourth place on 65.

Defending champion Ben Crane led a group on 66 that also included Tommy Gainey, Tom Gillis, Alex Prugh and Argentina’s Fabian Gomez.

Dustin Johnson, the highest-ranked player in the field at seven in the world, withdrew after nine holes because of an unspecified illness.