The wonder kid from Holywood in Belfast delivered the golfing equivalent of a Hollywood blockbuster, setting record after record at Congressional as he kept the trophy not just in European hands, but Northern Irish hands.
More than that, he became at 22 the second youngest European major winner of all time - and the youngest since 1872, the year Young Tom Morris captured his fourth and final Open at 21. He died three years later.
Not since amateur legend Bobby Jones in 1923 has this the toughest of all four majors been lifted by someone of such tender years - and with Padraig Harrington saying that McIlroy has the potential to challenge Jack Nicklaus's 18-major record it ought to be noted that the Golden Bear was a few months older when his first win came.
But the most remarkable thing is that it was only in April that McIlroy imploded at Augusta, seeing a four-stroke lead turn into a 10-shot defeat with a closing round of 80.
This was the first major since then and he was a class apart from the moment he started in the same way he had at The Masters with a 65.
By the time he had raised his arms in triumph to the roars of the crowd - such a contrast to the heckling that runner-up Colin Montgomerie received at the same venue in 1994 - everybody present knew they had witnessed something and somebody truly special.
Among the first to join in the celebrations was his dad Gerry. On Father's Day that was only right and proper.
Back at home there were the same joyous scenes that had greeted Graeme McDowell's victory 12 months ago - the first by a European in the event for 40 years.
They have all known about McIlroy's talent since he shot 61 at Portrush as a 16-year-old - and many of them for long before that.
With a closing 69 for a tournament record 16 under par total of 268 he set or shared 13 US Open records.
Whether he goes on to do more than Nicklaus or Tiger Woods, who won by 15 in 2000, should not detract from this achievement.
That statistic, inevitably, also said something about how soft the Washington course was all week, but it was the same for everyone and only one took full advantage.
Insistent that he had his Masters nightmare in context within a few days of it happening - he was third in Malaysia the following Sunday - a visit to earthquake-hit Haiti the week before coming to Washington added further perspective.
He still had to show, however, that regardless of his eight-stroke cushion with a day to go he was capable of remaining in a league of his own.
Lee Westwood, joint third overnight, started with a birdie, but in the group behind McIlroy matched it from nine feet and an approach to four feet at the 470-yard fourth made the gap double figures.
Yang got it back to eight on the two outward par fives and McIlroy had a narrow escape when his pitch to the long sixth only just made it over the water, actually bouncing off the wall of the water onto the green.
Asia's only major winner - he overtook Woods at the 2009 US PGA - then struck his tee shot to around three feet on the dangerous short 10th, but McIlroy not only got inside him, but almost holed-in-one.
Sharing it in birdie twos meant he was a step closer and McIlroy had, of course, improved five shots on what he took at Augusta's 10th that fateful day.
When Yang hit his second into water on the 11th and bogeyed victory seemed in the bag and, as if it had not been all weekend, the real battle was for second place.
And, as at The Masters, 23-year-old Day ended up as runner-up, a bogey-free 68 seeing him finish two ahead of a group including England's Lee Westwood.
His wait for a first major goes on and he did not quite do enough either to regain the world number one spot from Luke Donald.
McIlroy did bogey the 12th after driving into sand and, after another birdie at the long 16th, he did have his only three-putt on the 17th.
But it was all over long before then. The future of golf had arrived.