No question, adrenaline was pounding through his veins as he placed his ball on the tee for the opening shot of his final round.
However, the little smile which played on McIlroy's lips as he cast his eye down that sun-splashed first fairway showed his emotions and his expectations were well under control.
You see, McIlroy's been through all of this before, gleaning a world of experience and a tough hide from his final-round meltdown at last year's Masters and subsequent US Open win 70 days later at Congressional.
While most marvel at the effortless way in which he generates power with that honey-smooth swing, the real source of his strength lies in his speed on the uptake.
The most significant message from a remarkable week of steamy hot sunshine interspersed by howling ocean gales, teeming rain, and the intervention of an electrical storm after he'd played just nine holes of his third round on Saturday afternoon, is that McIlroy, the Major contender, is back.
After fulfilling one of his lifelong ambitions by loping to the top of the world rankings with victory at the Honda Classic in March, McIlroy then flopped when it really counted — in the season's first three Majors.
He flattered to deceive at the Masters, slumping out of contention during a disastrous front nine on Saturday and played for the rest of the weekend at Augusta as if somebody had pulled out his plug.
McIlroy didn't get beyond halfway during his US Open title defence at Olympic and made little impact at the Open, despite a nice first round 67.
It was concerning to see how easily the youngster's shoulders slumped so McIlroy's putting coach Dave Stockton (70), a two-time PGA Championship winner and captain of the US Ryder Cup team in the 1991 ‘War by the Shore' on Kiawah, decided to have a word with his pupil.
And McIlroy has been reborn at Kiawah.
Though Tiger Woods had good reason to be happy the storm moved in on Saturday after he'd played the outward half in four-over, he too would sign for a 74.
McIlroy wore red yesterday and seemed impervious to the slings and arrows hurled at him by his rivals.
When McIlroy birdied seven to go ten under, he led by four.
And he refused to buckle as Ian Poulter went on a hot run.
McIlroy sealed the victory and Northern Ireland has its own Major champion yet again.
McIlroy’s fellow Ulsterman Graeme McDowell (pictured) — the 2010 US Open champion — shot a closing round one under par 71 for a two under par total, just missing out on a top 10 finish.
The other member of Northern Ireland’s Big Three, last year’s Open champion Darren Clarke, fired a one over final round for a six over total.
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