Rory McIlroy holed nothing longer than a four-and-a-half footer on the final green as he carded a third-round 73 to fall nine shots behind Billy Horschel heading into the final round of the Memorial Tournament in Ohio.

The world number eight went into the day tied for fifth, just three shots behind Australia's Cameron Smith but lost more than two shots to the field on the greens.

Scores

As Horschel carded a seven-under 65 to lead by five shots from Smith (72) and Aaron Wise (69) on 13-under, McIlroy got to six-under with five holes to go.

But hit just one of the last three greens in regulation and bogeyed the 16th and 17th to finish the day tied for fifth on four-under.

The Co Down man was far from his best on a tough course but admitted the Jack Nicklaus-designed course required the ultimate in precision.

"Yeah, it's getting a little bit tricky," he said. "You've got to land it on your spots with your iron shots and you've got to put it in the fairway to get chances to get it close. Greens are getting fast, so having to play a little more break.

"It's hard to keep the ball below the hole, so you're -- there's a lot of putts out there that are a little bit defensive.

"Yeah, overall just getting a little trickier, but it's good. I think it's the way the golf course should play. It's perfect.

"I mean, it's tough, but it's fair, and obviously you see someone like Billy go out and you're still able to do that if you hit the shots and hole the putts."

Horschel has gone 44 holes without a bogey, carding a seven-under-par round for the joint-biggest 54-hole lead of the PGA Tour season.

Usually a quick, instinctive player, he's made a conscious effort with his caddie to slow things down, and it's working, as his five-shot lead attests.

"It's just going through our process, making sure we have a number where we're trying to land the ball, talking about the shot, the club selection, the wind," the 2014 FedEx Cup champion said. "When we do that, it allows me to have a clearer picture and have a little bit more of a higher acceptance level over the golf shot.

"I move very quick, and I'm impatient, and so I'm ready to go without always being clear on everything. Sometimes I just want to get the golf shot over with.

"Yes, I am an idiot for not doing what I know works every time. If I'm going to win the golf tournaments I want to win, and I feel like I can win, then I need to do a better job of it on a daily, weekly basis, especially when it comes to the bigger events."

Like McIlroy, Shane Lowry got into the red for his round heading down the back nine but bogeyed the par-five 11th after finding water off the tee, then found water again and double-bogeyed the par-three 12th.

He did well to pick up two shots coming home, but a level par 72 left him tied 19th on three-under-par.