Rory McIlroy makes steady start at FedEx St Jude Championship in Memphis

The Northern Ireland player is four shots behind early leader Jordan Spieth, who topped the leaderboard with a seven under par 63.

"It's probably the worst I could have scored," said McIlroy, speaking on Sky Sports.

"I drove the ball incredibly well and it could have been a lot lower."

American Spieth goes into round two leading 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.”

England’s Tommy Fleetwood and Aaron Rai were the best of the British contingent, closing out Thursday on four under par.

Meanwhile, Northern Ireland’s Stephanie Meadow was three shots off the lead in the AIG Women's Open at Walton Heath after the first day.

Cavan’s Leona Maguire also made a strong start to the event and is a shot further down on leader Ally Ewing of the USA, who shot a four-under round of 68.