McIlroy paid tribute to both his parents, who made huge sacrifices over the years to support their son's golfing ambitions. At one stage, Gerry worked three jobs, while McIlroy's mother, Rosie, worked nights in a factory.
'I can't thank them enough,' he said last night.
Taoiseach Enda Kenny described McIlroy's victory as both emphatic and inspiring, saying it ranks among one of the great achievements in any sport.
Minister for sport Leo Varadkar said McIlroy's performance confirmed the arrival of a new sporting hero.
No one was taking anything for granted this time -- after all, some of Holywood Golf Club's patrons were still nervous wrecks after Rory McIlroy's infamous Masters crash.
Sunday afternoons are usually more sedate affairs, but yesterday the club where McIlroy honed his stellar talent was thronged from early afternoon with hundreds of cheering supporters.
But the volume of the crowd was disguising some nervousness.
As they clambered round the screen, angling for the best views of the 22-year-old star as he took to the Congressional course, fingers were being crossed and prayers silently given up.
Stephen Crooks, Holywood's head club professional, was one of those left despairing after Rory's Masters disaster.
"I don't think anyone could handle that again. This time around he was just playing his normal game. It was an exceptional start for a US Open course set up as tough as this," he said.
"He's played aggressively, and it's paying dividends -- there is huge buzz tonight."
For most of those in attendance, yesterday was among the club's proudest moments in a history spanning 107 years.
The McIlroy family are part of the fabric of the old club. Rory's late grandfather Jimmy is still talked about in glowing terms and dad Gerry worked regularly behind the bar to fund his son's formative years in the sport.
His uncles, Colm and Brian, are members and cousin Fergus dreams of following in Rory's footsteps.
The club even bent its rules to let Rory in as a member at the age of seven, after a mandatory induction interview where "he assured us that he wouldn't be a nuisance to anybody and that he knew the rules", said Eddie Harper, who organised the juniors.
Close family friend Sam Gilpin said he was proud of how far Rory had come.
"It was a big disappointment for Rory after the Masters. I've known Rory since the day he was born and I've been to Dubai and other places to watch him as an amateur and a pro," he said.
"He has been an ambassador for the club and has been taught from an early age how to deal with the media and money.
"It is no surprise to us at Holywood how successful he has been -- just how quickly it has happened."
Andy Rice has been a member of the management committee at Holywood Golf Club on Nuns' Walk for the last 10 years.
"It has given everybody something to smile about," he said, "and it's a super Father's Day present for Gerry."
Little Jack Cardy (11), goes to Rory's former primary school, St Patrick's primary in Holywood. He counts among his most prized possessions a signed hat and hopes to follow in his hero's footsteps.
"He is really cool, and I hope I can play like him some day," said the aspiring golfer.
Back in April many of the same faces looked on through clasped hands as jubilation turned to dejection when McIlroy's US Masters dream collapsed emphatically.
Holywood Golf Club was inundated with letters of support in the days following the US Masters debacle, which Rory collected from the club and took home to read.
He had vowed to prevent a repeat this time around, again going into the final day with a seemingly unassailable lead.
Universally described as a level-headed ambassador for the club, those closest to Rory say there is no chance of him forgetting his roots.