Australian Day, 27, leads the tournament by two shots from Spieth after a third-round, six-under-par 66 and will have to go in search of his first major success in a head to head with this year's Masters and US Open champion, who stormed into contention with a blistering back-nine 30 to post to a 65.

Day stands at 15 under par with Spieth, bidding to become only the third man to win three majors in a calendar year after fellow Texan Ben Hogan in 1953 and Tiger Woods in 2000, joining him in the final pairing of the day on 13 under, teeing off at 7:45pm Irish time.

Branden Grace of South Africa and England's Justin Rose will start the final round a further shot back on 12 under, Grace having shot a 64, while Germany's Martin Kaymer is poised on 11 under to try and repeat his victory here by the shore of Lake Michigan in the 2010 PGA Championship.

World number one Rory McIlroy will need to shoot something spectacular if he is to make inroads from six under par but he is moving in the right direction after firing a 68 on Saturday, his best round of the week since returning from an ankle injury.

The Irishman will have a massive incentive to maintain pressure on the leaders, however, as Spieth threatens to usurp him as the highest ranked player in golf. The 22-year-old can overtake McIlroy, currently tied for 17th on the leaderboard, if he maintains or betters his second-place position in a number of scenarios.

The odds will favour Spieth, however, after his stunning final nine holes in his bogey-free round on Saturday night, holing six flawless birdies including the last three holes. Not that his goals stretch beyond simply winning the tournament.

“Just to try to get my name on the Wanamaker Trophy, that's about it, that's the only history I'll be thinking of when we step on the first tee is you can hoist that trophy tomorrow and make it happen,” Spieth said.

“This isn't as much in my head off the course as it was to try and get the Grand Slam, when I was getting ready to shoot for it the last couple of days at St Andrews. At this point it would be really cool, but it isn't a Grand Slam.

“So for me it's going to be the same kind of just same level of focus as I'm sleeping tonight, I'll sleep just fine. And I'll go into tomorrow strictly for the history piece of trying to get my name on a different major. It's a goal of mine to capture all four throughout my career. I've got a great opportunity to get the third right now.”

Day, with nine top-10 major finishes in just 20 starts, may have something to say about that as he bids to land his first win.

“My confidence level is high,” the Australian said, “but I'm just more enjoying just being out on the golf course, rather than in previous positions that I've had in Major Championships, I've viewed them as very stressful and kind of hard to go out and play the next day.

"But I'm enjoying myself so much on the golf course. It's been fun to be out here in pressure situations. It's good to be in contention, especially on Sunday. It's good to have the lead, so that's a plus.

“To be able to do what I did, especially on the last three days, put myself in position here, I've done what I need to do, now I've just got to focus on round four and just kind of keep pushing forward.”

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