Even by McIlroy's standards of sorcery, the ensuing comeback was astonishing. Prior to Fitzgerald's intervention, he had exuded a woebegone air, rubbing his eyes and realising this was not quite as he planned it.
One moment, he had been urging punters to pile on him at pre-Open odds at 20-1, a mischievous gleam in his eye suggesting he knew more than the market.
The next, he was scrambling to drop just one stroke at the first, after his ball plunged deep into the fescue. The grisly tailspin that ensued made it look for all the world as if his prospects of a fifth Major title had gone in 60 minutes.
Thank his trusty bag-man, then, for helping him restore contact with his true self.
For this was a day when McIlroy blew as hot and cold as the swirling Birkdale breeze. He is not known for his cussed rearguard actions in adversity, but somehow, despite an hour of torment, he turned a potential 78 or worse into a 71 that kept him at the beating heart of this championship.
Slumped shoulders gave way to that jaunty, bouncy gait that he displays whenever he senses he still has a chance.
It was a strange, lopsided scorecard - 39 strokes out, 32 strokes in - but the most celebrated players can take such setbacks in their stride.
Tiger Woods shot 40 for his front nine on the first day of the 1997 Masters and 30 for the back, and he ended up winning the tournament by 12.
Fittingly, McIlroy regarded his own position, just six behind the leaders, with supreme nonchalance.
"I was four over through three holes in Boston last year and I won there," he shrugged. "I've done it before."
Seldom, if ever, can a golfer of his gifts have been so cock-a-hoop at reaching the clubhouse at one over.
Such is the rejuvenating power of an unexpected final flourish. For a few wretched holes, McIlroy had appeared as though he could not find a fairway if it had been painted fluorescent pink, but as he headed for home, his iron shots re-acquired their familiar towering majesty.
Thanks to a pair of birdies to close, he beamed for the cameras like a man who had just set a course record.
"I could be standing here, having hit 18 greens and missed every putt, and feel terrible," he said.
"But considering the way I started, I feel positive. It's a bit like the Ryder Cup at Medinah in 2012, being 10-6 down on the Saturday night, but still feeling that we were right in with a chance, because we had won the last two points.
"In any other circumstances, it might have been a disappointing day, but because of the way it finished, I feel great."
How satisfying it was, too, to prove the naysayers wrong.
After a mere two errant shots on Friday (New Zealand time), Sir Nick Faldo claimed on US television that he had "heard through the grapevine" that McIlroy was a troubled soul.
"I don't think Rory's settled," he said. "There's a lot going on in his life, too much."
Whatever that meant, McIlroy, who has seemed blissfully contented off the course since his marriage earlier this year to Erica Stoll, found his own way to brush off the conjecture.
Weighed down by expectation at the outset, he had invented himself, come sunset, as golf's strutting alpha male.
McIlroy stopped afterwards to offer an unusually candid insight into his complex state of mind.
One might suppose that a player with four Majors by the age of 28 would be impervious to pressure, but he disclosed that he had been consumed by nerves.
"I was anxious, timid, thinking 'Geez, here we go again'," he said. "But I knew that I needed to stay patient, stay with it. I didn't get angry out there, I didn't let my head drop too much.
"I kept a positive attitude and thankfully it turned around for me."
Asked about the root of his apprehension, he explained: "There was just a lack of confidence, with what has happened lately."
It has taken time for McIlroy to rebound from a rib injury and he acknowledged in recent days that the stiff winds were playing havoc with his alignment over the ball.
"I let all of that get into my head. It's a Major championship and you're desperate to shoot a good score.
"I'm always more nervous playing a links than I am any other course. There was a lack of self-belief.
"Somehow, I was able to find it again halfway through."
From the edge of Birkdale oblivion, he was back in the game. There should be no understating the significance of the shift.
McIlroy's peers will know from bitter experience that he is at his most dangerous, when he has the wind in his sails.
