Ninety minutes later he faced the burden of keeping some of the biggest stars in golf at a distance and slugging it out with soggy Valhalla Golf Club to win the 96th edition of PGA Championship.
Two hours into his final round, he had lost the lead he earned through the tournament's first 54 holes and looked puzzled as his game looked frazzled.
The world's No. 1 player finally gathered himself and remained collected the rest of the way as fireworks exploded on the prairies and backwoods of the Bluegrass State.
Barely beating the setting sun and approaching thunder and lightning, McIlroy held off Rickie Fowler, Phil Mickelson and Henrik Stenson to win the last major of the season.
Ignited by an eagle from 7 feet on the par-5 10th hole, and basically slamming the door shut on his competitors with a birdie from 10 feet on the 17th, the former Boy Wonder won his fourth major of his young career, three of them in his last nine starts and two in his last two.