The 23-year-old Northern Irishman began his defence of the US Open title with a seven-over-par 77 last night.
It left him 11 strokes behind shock leader Michael Thompson - a 27-year-old American qualifier - and not even in the top 100.
Only the leading 60 and ties after the second round continue into the weekend, organisers having scrapped the rule whereby anyone within 10 shots of the lead at halfway also stays alive in the event.
The only positive thing that could be said was that McIlroy still scored one better than Masters champion Bubba Watson and two less than world number one Luke Donald.
"It's just so tough here if you put yourself out of position at all," said McIlroy after initially declining a request to speak to reporters.
"Too many times I just was in the wrong position off the tee or with my second shot.
"When you're trying to play catch up on this golf course it's very hard. I was able to make one birdie - I need to try to make more tomorrow and limit the mistakes.
"But you have to be so precise. Anything just a little off and it really punishes you.
"I tried to approach it like any other tournament I play and tried to go out there and shoot the best score I could.
"It wasn't my greatest day, but hopefully I can come out tomorrow morning and try and shoot a good one and at least try to be here for the weekend."
Donald could not hide his disappointment after failing to make a single birdie in his 79.
McIlroy, an eight-shot winner with a record 16 under par score last year, was playing with Donald and Lee Westwood, who after a double bogey on the first battled hard for a 73.
Donald, his search for a first major win looking almost certain to go on to next month's Open at Royal Lytham, said: "In the US Open the margins are that much smaller and if you're just a little bit off it's tough.
"My putter kind of went cold, otherwise I could have probably ground out some more respectable score.
"The top three in the world and we make three birdies between us - it shows how tough it is.
"I tried to stay patient, tried to stay positive, but when I had those opportunities on the greens I couldn't take them."
Asked whether the trio had tried to gee each other up he added: "We were focused on ourselves mostly.
"There was a little bit of chat out there, but not too much. The US Open demands your full attention and obviously Lee had a good back nine (one under after all three turned in four over), but Rory and I both struggled."
Thompson, runner-up in the US Amateur on the course five years ago and ranked 107th in the world, leads by three just as McIlroy did after the opening round in Washington.
He covered the last 12 holes in six under for his 66 and said: "This is just a bonus in my career. I'm not guaranteed into all the majors and to have the opportunity is just a wonderful experience."
With McIlroy and Donald faring so poorly Tiger Woods has become an even stronger favourite.
His 69 was good enough for a share of second place with 2010 winner Graeme McDowell, England's Justin Rose and two more Americans, Nick Watney and David Toms - Watney after sinking a 190-yard five-iron on the long 17th for only the third albatross in US Open history.
McDowell and Rose both finished with a brace of birdies late in the day to give the 36-strong European contingent a presence on the leaderboard.
"I made a great up-and-down from the front trap on 17 and managed to cosy it in there about 15 feet on the last," said McDowell, whose victory two years ago came down the Californian coast at Pebble Beach.
"I've always enjoyed the US Open, even before I won. It really rewards placement off the tee, just hanging tough, staying patient. Really it's golf's toughest test.
"You've got to play very kind of workmanlike golf at times. I watched a bit of the coverage this morning and saw the way Tiger kind of played.
"He just did what this course asks you to do. You've just got play very disciplined golf.
"You want to get a little bit of momentum because if you let this course beat you up early in the week it will just continue to do that."
Told about McIlroy's 77 he said: "Seven over's a big hole for any player. If anybody can come back from it he can, but this course doesn't really offer up many 64s."
Rose, winner of a world championship in Miami in March, said: "It was fun out there. You had to hit great shots to keep it in play and to get it close to the hole.
"You can't get ahead of yourself for one second out there. It's going to be a long, hard week ahead of all of us and that's really my mindset.
"It's sort of sadistic fun. Mediocre stuff gets penalised for the most part."