It will go down in golfing folklore as the day Rory McIlroy, a bright working class lad blessed with the swing of an aristocrat, proved to himself and showed the world he has the heart and soul of a streetfighter.
McIlroy won a second US PGA title and his fourth Major championship in Louisville, but on one of the most thrilling Sunday afternoons in the sport's history, he became legend.
The 'Tiger Era' formally ended and the 'Rory Epoch' dawned.
The heavens might have poured torrents of rain on Valhalla but once the monsoon stopped, all the thunder came from the packed galleries as McIlroy, Phil Mickelson, Rickie Fowler and Henrik Stenson hurled veritable lightning bolts at each other across sodden fairways.
In the midst of it all, the 25-year-old world No 1 faced one of those pivotal moments which the truly great champions encounter on the road to fulfilment. Stripped of his lead and wallowing at two-over after his second bogey of his final round at the sixth hole, McIlroy faced a stark choice.
Give in to the exhaustion or pick himself up and fight. He chose the latter and over the next 12 holes proved to his rivals and the watching world that this fresh-faced kid from Holywood, Co Down, has become 'The Man'.
Each of his Major victories were remarkable in their own special way. That record-shattering first in the 2011 US Open at Congressional remarkably came just 70 days after McIlroy's crushing implosion at the Masters.
His second runaway win in the 2012 US PGA at Kiawah brilliantly obliterated any doubts sewn during that summer of discontent, while last month's Open victory at Hoylake was achieved as much through patience, maturity and persistence as instinct and raw talent.
As he lifted the Claret Jug, it was clear McIlroy had become master of his own destiny.
Yet in Sunday's blood and guts battle across the lush green fields of Kentucky, McIlroy showed not only that he has the 'moxey', as Jack Nicklaus described it, to win ugly but also the same ability to influence and maybe even intimidate others as Tiger and the Golden Bear.
"To win in this fashion, in this style, means a lot to me," he said. "It means that I know I can do it. I know I can come from behind. I know I can mix-it in a dogfight down the stretch in a Major with the top players in the world and come out on top.
"Phil Mickelson is the second-best player in this generation and to be able to beat him on the back nine on Sunday is great to have in the memory bank going forward."
As for that near-mystical power to make others look nervously over their shoulder, he said: "I sort of felt like it today. Rickie made a bogey on 14 and then made another on 16. Phil made a bogey on 16.
"I'm not saying my name on the leaderboard in any way affected them but it has to do something, especially with the play I've produced over the last few weeks. It's just another thing to have in my locker, knowing that If I get my name on the leaderboard maybe it'll affect the other guys."
In the past month, McIlroy has soared in the golfing firmament, becoming the third youngest player, behind only Woods and Nicklaus and ahead of Seve Ballesteros, to win four Majors. He has now won as many at age 25 as Ernie Els, Vijay Singh and Raymond Floyd did in exalted careers spanning decades.
Naturally, he's aware of his status in the game but dismisses such thoughts almost as soon as they arise. "There are only two players active in the game who have won more Majors than me, Tiger Woods and Phil Mickelson, but that's something I try not to think about too much."
While Woods has been driven throughout his career by the pursuit of the record 18 Majors won by Nicklaus, McIlroy has consistently set himself only short-term goals, a disciplined approach which he rigorously applies on the golf course as well.
In keeping with this shot-by-shot, hole-by-hole, Major-by-Major philosophy, McIlroy identified next April's US Masters and his desire to join Nicklaus, Woods, Player, Hogan and Sarazan in completing a career Grand Slam as his primary ambition.
Consequently, he also wants to equal the five Majors won by Seve Ballesteros, while setting himself the slightly longer-term target of one day beating Nick Faldo's six
Looking forward 242 days to Augusta (a figure he saw in a Tweet posted by Jason Day, incidentally), McIlroy said: "There's going to be a lot of hype for sure. It's the only Major I haven't won and I desperately want to get that Green Jacket. I'm not going to try too hard but I know if I play my game and play the golf I'm capable of, I will do. There's no reason why I shouldn't think I can win the Masters."
Though determined to take a week out to toast properly with friends and family his heady first hat-trick of victories in the Open, at Firestone and in the US PGA, a feat previously achieved only by Tiger (in 2000 and 2006), McIlroy's ambitions for this season are far from sated
The FedEx Cup play-off series starts next Thursday week with the Barclays and, naturally enough, McIlroy covets the title of PGA Tour champion and the $10m bonus that goes with it .
"Look, I'm playing some great golf at the minute and want to keep this run going as long as I can," he explained. "First and foremost is the FedEx Cup. I came close a couple of years ago and didn't quite get the job done but I feel like my game's in good enough shape that I can try and win that.
"Obviously I want to go into the Ryder Cup in Gleneagles in the best form possible and to finish off the season as well as possible. I've got a couple of tournaments in the Far East, the Race to Dubai and then I'm going to defend the Australian Open title and that'll be me done for the year."
Given the courage he showed on Sunday in fighting his way out of one of the tightest corners in his career, few if any of his rivals would fancy their chances against McIlroy right now.
McIlroy is driving the ball spectacularly well. Remarkably, with little run on soft fairways, he topped the charts with an average 315.6 yards off the tee. So intense has McIlroy's commitment to the gym been in recent months he has piled on nearly seven pounds of muscle. However, his mental strength was key on Sunday.
Admitting he'd felt 'flat' over his opening holes as fatigue from his feats at Hoylake and Firestone were compounded by an intense week in Kentucky and exacerbated by the 110-minute rain delay to the start of play, McIlroy initially wilted in Sunday's oppressive heat and humidity.
There was a telling scene when he flopped down onto the bench at the back of the sixth tee. The play was bunched up and painfully slow at this point, forcing McIlroy to wait before playing many of his shots.
Fowler, playing with Mickelson in the group ahead, was about to hit his tee shot when he turned, caught McIlroy's eye and grinned broadly. At that point, the Californian had plenty to smile about after three straight birdies put him in the outright lead.
When he followed a rare three-putt bogey at four with with another dropped shot at six, McIlroy's shoulders didn't slump as they might have in the not-too-distant past. Instead, he took stock of his situation and found the hero inside himself.
"I really needed to dig deep. To be up there with the lead week-in, week-out and trying to win these big tournaments is tough mentally and physically but I just told myself, you have 12 holes left, you can take a week off after it, just try and put everything into it," he said.
The birdie he desperately needed then came, courtesy of an ingenious lob-wedge to inside three feet after shortsiding himself badly behind a greenside bunker at seven.
Fortune favoured McIlroy on 10. Trailing Fowler by three as he stood in the fairway on this par-five, he necked his three-wood "probably 30 feet lower and 15 yards to the left of where I intended" but the ball hopped, skipped and scuttled 272 yards up to seven feet. This eagle restored McIlroy's predatory instincts and transformed his rivals into his prey.
Between his fist-pumping birdie at 13 and another at 17, where he played a masterful shot out of a fairway bunker to 11 feet, Mickelson, Fowler and Stenson all faltered.
The tournament ended in near farce and complete darkness as the final two groups played the last as a virtual fourball but even in the glooming, McIlroy shone like a beacon.
As golf acclaimed the dawn of the 'Rory Era", McIlroy made light of the burden. "I think your have to expect it and accept it if you have a run of golf like I have," he said.
"It's a great place to be in, to be one of the faces of golf. It's a big responsibility but I feel I'm up to the task of handling it well."
Agents and sponsors come and go as surely as the Portrush tide, but for Rory McIlroy one precious constant endures in the form of a gentle, red-haired, reticent figure who two years ago could still be found charging £40 a lesson on the outskirts of Belfast.