As world number one Scottie Scheffler tried but failed to catch McIlroy, a song echoed around Holywood.
“He’s in your head, in your head, Rory, Rory, Rory, ” sang the fans, to the tune of Zombie by the Cranberries.
Leading the chorus were teenagers who went to McIlroy’s old school, Sullivan Upper.
Among those in awe of his resilience, and brilliance, was 18-year-old Oliver Keown.
“I’m amazed, I’m stunned,” he said.
“When he double-bogeyed the fourth hole I was starting to get a bit nervous but he came through and still won.”
Hamish Johnston, also 18, said: “I never doubted him. He’s world class.”
Among the dozens of other golf fans in the packed clubhouse was Leah James.
She too had total confidence in the 36-year-old Holywood golfer.
“Why would I doubt him? He’s one of us,” she said.