Jordan Spieth topped the leaderboard after round one of the FedEx St Jude Championship, where he scored seven under par with a bogey-free 63.
The American goes into round two in Memphis leading South Korea's Tom Kim by one shot and admitted he has been working on his putting.
“Quite a bit of putting. I played really well at the British. Tee to green, I played well enough to win,” he said afterwards.
“I didn’t feel like I missed many of my lines. I just couldn’t quite get the matching of the line and speed on the greens.
“Now we come to slopey Bermuda and very fast slopey Bermuda where I feel a little more comfortable picking lines and kind of feeding the ball in using gravity.
“I think that helped, along with quite a bit of work as best I could in Texas right now, which is really from the hours of 7:00 a.m to noon before it’s almost unbearable.
“Just tightened some things up. I tried to play a lot just to shoot scores. I had kind of taken off playing a bunch, and I think that that helped a bit in the last couple weeks.”
Argentina's Emiliano Grillo and American Collin Morikawa both carded 65s for a share of third place at 5-under.
England’s Tommy Fleetwood and Aaron Rai are the best of the British contingent, closing out Thursday in fifth place on four under par with eight other players.
Rory McIlroy sits a shot back on three under, after he split three bogeys with four birdies and an eagle.
"I don't know if I can remember a round where I've driven it that well, at least in recent memory," said the Northern Irishman. "I drove it really well today and gave myself so many looks from the fairway.
"Sort of walking off the course disappointed with 3-under. I felt on another day when I have been on song a little bit more, especially with the putter, it could have been a 63 or a 64.
"You know, it was a slow start, and then the eagle on 16 sort of got me going.
"I played solid. I just feel like I left a few out there."
