McIlroy, whose resounding wins at the 2011 U.S. Open at Congressional and last year's PGA Championship on Kiawah Island and a climb to the number one ranking cemented him as golf's next prodigy following in the wake of Tiger Woods.
But a tumultuous season of distractions, challenges and missteps has McIlroy, last year's leading money winner on both the U.S. and European tours, winless and groping to find his top form heading into the year's second major.
"I haven't lived up to my own expectations this year," the 24-year-old McIlroy told reporters at the Memorial Tournament, where he tied for 57th in his last event before the Open.
"But I'm working hard to try and get the game back to where I know it can be."
Change seems to be the word one can apply most consistently to the mop-haired McIlroy of late.
Last year he put his Belfast house up for sale and bought a house in Florida to serve as his PGA Tour home base.
He launched this season by signing a $100 million-plus sponsorship deal with Nike, making a ball and golf club equipment change from the Titleists he used when romping to eight-stroke victories in both his major triumphs.
Twice he has changed management firms in the last two years, having now formed his own management company with his father, Gerry, taking a key role.
The strains of expectation and frustration with his form led McIlroy to a serious faux pas on the playing course in March when he walked off mid-round at the Honda Classic in exasperation at his poor play and later blamed the exit on an aching tooth.
He later apologised, taking another knock in the awkward challenge of growing up in public view on the world stage.
With all that going on, no one doubts what McIlroy is capable of any time he tees off, and there is nothing like the challenge of a major.
"I guess I approach majors with just that little bit of a different intensity level because you have to," McIlroy said.
"You get four chances at it a year and you want to put everything you've got into it. And luckily I've been able to win a couple the last couple of years. And it would be nice to continue that trend this year."
McIlroy will have to deal with the harshest spotlight imaginable over his first two rounds at Merion.
He is grouped with Woods and Australian Adam Scott, the reigning Masters champion, in the U.S. Golf Association's feature threeball made up of the world's top three ranked players.
"Decent group for the first 2 rounds at Merion I see..." McIlroy tweeted after the draw was announced.
McIlroy and Woods have played together 12 times in competition, but never before in a major. Woods has recorded the better score on nine occasions.
Woods, dealing with his own five-year drought without adding to his majors haul of 14, knows what McIlroy is capable of.
Last year, the Northern Irishman went into a mid-season tailspin missing four cuts over five tournaments before dominating the PGA Championship at the Ocean Course.
"We all know the talent he has," Woods, who has reclaimed the world number one spot from McIlroy this season, said after the 2012 PGA.
"We all go through those spells in our careers. He's got all the talent in the world. When he gets it going, it's pretty impressive to watch."