JT Poston surges clear at Memorial as Rory McIlroy and Scottie Scheffler struggle

McIlroy struggled on the slick putting surfaces, carding a two-over-par 74. His round featured three bogeys and a costly double-bogey at the par-four 13th, where he required five strokes to hole out after finding himself 112 yards from the pin.

The Northern Irishman sits 10 shots adrift of Poston's lead and Scheffler is in the same position after posting an even-par 72, later admitting his score could have been far worse, saying he "could have shot 90".

"Overall it was a tough day, I felt I could have shot 90. I may be a lot of things but I'm not a quitter," he said.

"That's maybe some of the worst I've hit it in a couple years out there and I still managed to shoot even par around a golf course that requires you to strike the ball really well."

Poston separated himself from the field with a superb seven-under-par 65, a score unmatched by any of his rivals and four strokes better than the next-best round of the day in Ohio.

Meanwhile, Tommy Fleetwood failed to build on his share of the overnight lead, slipping back after a one-over 73 left him tied for fourth place and five strokes off the pace.

"It was pretty brutal, actually. I still think I got a good score out of that today. I made a bogey on one and six, where I didn't really feel like I had done anything wrong whatsoever," he said.

US PGA champion Aaron Rai and compatriot Alex Fitzpatrick sit in a tie for ninth at one under par after rounds of 70 and 71 respectively. They are joined by Ireland's Shane Lowry, whose eventful 73 included five birdies but was undermined by two double bogeys and a further two dropped shots.