Irishman and world number 192 Paul Dunne has won the British Masters, his first European Tour title.
Dunne, who sprang to prominence after sharing the 54-hole lead in the 2015 Open Championship while still an amateur, fired seven birdies and an eagle in a closing 61 to finish 20 under par.
And the 24-year-old sealed victory in style by chipping in on the 18th to finish three shots clear of McIlroy, whose 63 was the lowest score of an injury-plagued season.
Dunne enjoyed a remarkable stroke of luck when his approach to the 11th pitched into a sprinkler head on the edge of the green and bounced back to within five feet of the hole.
But the good fortune was well deserved after the 24-year-old played the first six holes in five under par to move into a lead he would never relinquish, with the victory - worth £500,000 - lifting him into the world's top 100 for the first time.