But Austrian Bernd Wiesberger heads a pack of eight players all within four of the leader after a superb round of 65.

McIlroy, the world number one, finished the day as he started with a one stroke advantage and negotiated the front nine with two birdies and a bogey at the eighth.

The 25-year-old was not at his imperious best, however, and dropped another shot at the 12th after some uncharacteristically wayward approach play, but he regained his composure and rhythm to rattle in three birdies from the last four holes to remain out in front on 13-under-par going into the last day in Kentucky.

"It's not the biggest lead I've ever had but I am still in control of this tournament," said McIlroy, aiming to become the first player to win back-to-back majors since Ireland's Padraig Harrington in 2008.

"It is where I want to be.

"I wouldn't want to be anywhere else.

"It is a great position going into tomorrow.

"It is stressful times, but you have to enjoy it because it is the best place to be.

"I just knew I needed to make a couple of birdies on the back nine.

"The two birdies on 15 and 16 were huge, and to get up and down at 18 was big.

"It is not that huge a difference to be tied or have a one-shot lead, but it makes me feel better going to bed tonight."

Austrian Bernd Wiesberger is the surprise package at Valhalla as he goes into the final round just one shot off the lead ©Getty Images



McIlroy will be joined in tomorrow's final pairing by Wiesberger, who shot the joint-best round of the day to come racing up the leaderboard and put himself right in contention.

The Austrian has only two European Tour wins since turning professional in 2006 and has missed the cut in four the five previous majors he has played in.

But two opening rounds of 68 at Valhalla were followed by a six-under-par 65, highlighted by three successive birdies at the closing three holes to leave Wiesberger in outright second on 12-under.

"I played beautifully today, I didn't miss a lot of shots, set up a few nice opportunities on the last few holes especially," said the 28-year-old, ranked 70 in the world.

"I'm very proud of myself the way I played."

Wiesberger was playing alongside five-time major champion Phil Mickelson of the United States, who went round in 67 to sit at 10-under for the tournament where he is joined by Jason Day.

The Australian teed off one behind McIlroy and an eventful round saw him pick up four birdies but drop shots at the sixth and 16th.

Jason Day had to go searching in the long stuff after a wayward tee shot at the second hole at Valhalla Golf Club ©Getty Images



He made an unlikely par at the second hole after a wayward tee-shot saw him forced to wade across a creek known as Floyd's Fork to find his ball in the thick rough, before playing two superb iron shots to set up a putt for par which he made for an unlikely save.

American Rickie Fowler continues his consistent form in this year's majors as he sits on 11-under for outright third after a bogey-free 67 left him just two behind the leader.

South African Louis Oosthuizen, who won the Open Championship in 2010, leads a group of four players at nine-under-par that includes Henrik Stenson of Sweden, Finn Mikko Ilonen and Ryan Palmer of the United States.

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