The world number one had performed less than his recent spectacular best before producing three birdies over his last four holes to edge to the top of a crowded leaderboard with a four-under-par 67 and take a one-stroke lead at 13 under par into Sunday's final round.

Just 18 holes now stand between McIlroy, 25, a third straight win following his victories at last month's Open Championship and last Sunday's WGC-Bridgestone Invitational.

Austria's Bernd Wiesberger, a shot back on 12-under following his 65 on Saturday, will provide McIlroy's direct opposition in an all-European pairing in the last group to tee off their final rounds at 7:50pm Irish time.

But it will be more than a Sunday duel in the sun as American Rickie Fowler lies just two shots behind the 54-hole leader while Australian Jason Day and US star Phil Mickelson are three shots back at 10 under and further seven players are within five shots of the lead.

All of which means McIlroy's closing birdies at 15, 16 and the par-five 18th were particularly crucial on a day in which the scoring on a rain-softened par-71 course was the lowest of the tournament so far and the Holywood golfer had not been firing on all cylinders having taken a one-shot lead into round three.

“It wasn't as easy as I expected it to be out there today,” McIlroy said. “You know, they tucked a few pins away, and obviously playing with the lead, as well, you maybe can't play with the freedom as if you're chasing.

“But really happy with how I finished; to shoot another 67 without really having some of my best stuff for the round was really pleasing.

“I finished well and I noticed a few guys in front of me were sort of making a run on the back nine charge, noticed Phil was making a few birdies and Rickie was obviously making a charge and Bernd Wiesberger.

“I knew I needed to do something in the last few holes and to pull a few birdies out like that was really pleasing. I'm happy that I kept the lead going into tomorrow.”

To shoot a four-under-par round to stay atop the leaderboard having not played his best golf says much about McIlroy's confidence levels right now and one-putting nine of his last 12 holes contributed amply to the cause.

Furthermore he will go into the final round knowing that of the four times he has held a 54-hole lead at the Majors, he has converted them into victories each of the last three times, the exception being the 2011 Masters.

“The last two days, I haven't been quite as good as I can be,” he said.

“If everything does click tomorrow, then obviously I feel like there's a very low score in me. I'll take sort of scrapping it around in 67 if it puts me in this position again.”

The Ulsterman is now 45-under-par for his last 11 rounds stretching back to round one of The Open at Hoylake and in winning his last two tournaments he was won both by hanging onto his lead, when holding off the charging Fowler and Sergio Garcia to lift the Claret Jug, and coming from behind, as he did in making up three shots on Garcia at last Sunday's WGC-Bridgestone.

If he closes out the deal at Valhalla today, he will not only be the first back-to-back winner of Majors since Padraig Harrington won the 2008 Open and PGA, he will also be the first to match Tiger Woods in 2000 and 2006 in completing a triple crown of Open, WGC-Bridgestone and PGA victories in succession.

[comment]PGA Championship Round 4 Tee Times from Golf and Course

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And if victory and a fourth Major title does come McIlroy's way having dragged himself back into the lead from a five-way tie for the lead at 10-under, the manner of his success will not matter one bit for a golfer who won both the 2011 US Open and 2012 PGA by eight shots apiece, and the 2014 Open by two.

“I'll win any way,” he said.

“I'll take a win any way it comes. If that means having to scrap it out with a couple people coming down the stretch or if I can give myself some sort of lead going down the back nine or whatever it is... any win would be very satisfying.

“I won from three back last week. I feel like I'm in the best position I can be in going into tomorrow. I would rather be the guy that's being chased and have that shot advantage than not.

“Of course it's different. At Congressional (2011 US Open), I had the eight-shot lead. I think I had a three-shot lead going into Kiawah (2012 PGA) and then a six-shot lead going into Hoylake there.

“You know, three shots isn't really that much, either, if you think about it and I was sort of able to pull away from the field there.

“Tomorrow standing on the first tee is going to feel different than how it felt a month ago at Hoylake, because it is going to be a shootout.

“The conditions are soft; guys are going to make birdies, and you know that you're going to have to make birdies as well, to try and win.”

McIlroy has one more round to complete a remarkable run of success and he admitted Sunday's final day at Valhalla will be a trial, both mentally and physically.

“I've got one more day. I've got one more day to give it everything I have,” he said after his third round on Saturday night.

“Of course it takes a toll. It takes a toll mentally. Physically, as well, because you know you're not teeing off until pretty late and you're not getting back to your house until, it's quarter to eight now, so I won't be having dinner until maybe nine o'clock. It puts you out of your routine a little bit.

“But I've got one more day to just give it everything I have, and then I can take a week off and recover and then get right back at it and play another four weeks in a row!

“It's more mentally and physically tough whenever you're at this end of a leaderboard, especially a few weeks in a row.

“But I gave myself Monday off here this week and I still feel pretty fresh going into tomorrow. Hopefully that won't play any sort of part.”