Graeme Storm thought he had lost his European Tour card after the final regular-season event of last year in November, but was given a reprieve when US star Patrick Reed had to give his up because he had not played the required number of tournaments.
Fast forward to this weekend and the 38-year-old Englishman capitalized on his good fortune by beating world No. 2 McIlroy in a playoff at the South African Open.
It elevated him from 251 to 133 in the world rankings.
Storm, whose only other Tour win came at the 2007 French Open, won with a par at the third extra hole after his illustrious opponent missed a seven-foot putt to make a bogey.
"I am in shock," Storm said after his unlikely triumph, having seen McIlroy erode his three-shot overnight advantage Sunday at the Glendower Club in Johannesburg.
"What can I say? This is surreal. I have just beaten a golfer who is the best in the world right now.
"This is a dream come true after nearly losing my tour card. The whole experience this week has been absolutely incredible."
McIlroy, who battled a back problem which required anti-inflammatory tablets, shot a final-round 68 to Storm's 71, but struggled throughout the playoff with wayward shots off the tee.
"Obviously, it's disappointing to finish runner-up but Graeme played well all week and what a story for him," said the Northern Irishman, who will have a scan on his back ahead of this week's Abu Dhabi Championship.
'It's not a bad way to start the season and obviously something to build on in the coming weeks," he added.
McIlroy was the star attraction at a tournament hosted by South African great Ernie Els. It's the second oldest national open after Britain's Open Championship, dating back to 1893.
Four-time major winner McIlroy has set his sights on success at April's US Masters to complete a career grand slam and regain top spot in the rankings, currently held by Australian Jason Day.
England's Jordan Smith finished one shot out of the playoff on 17-under 271 after a closing 68, with Dean Burmester the best-placed home golfer, two shots further back in fourth spot.