McIlroy managed three birdies but twice as many bogeys in superb conditions on the Glen Oaks course, which was hosting an event of any stature for its first time since being opened in 1969.
The defending FedEx Cup champ birdied two of the opening par threes, holing putts of 29-feet at the second and clearing the water at the sixth and landing his tee shot to four-feet.
However, his front nine was very much a case of each time he did manage a birdie he proceeded to drop a shot.
Then over his inward half McIlroy dropped shots at the 10th and 13th holes while he found the water left of the green at the par three 17th taking the sixth bogey of his day.
“This is a new course for all of us so you do have to get to know it a little bit but then if you don’t find the fairway, given the rough is thick, you will struggle”, he said.
“Over the front nine I didn’t feel as though I played that well but still managed to scrap it around in level while the back nine I felt like I started to play a bit better but was three-over on that side.
“Though some of the pins positions were tricky located as they were on little sort hills and it was hard to get it close but then that is no excuse for shooting three-over par but it was pretty tricky.”
In fact, McIlroy hit eight of 14 fairways, a dozen of the 18 greens in regulation and after a lengthy session Tuesday afternoon with Phil Kenyon he had 30 putts.
It was a year ago at nearby Bethpage Park that McIlroy first began working with the UK-based Kenyon.
“I am working on a few things technically with my irons and I did struggle with my driver,” he said.
“So, it does feel a bit better with the irons but I struggled with the driver as it is harder with the longer club, and to have to have those technical thoughts and think about it a little bit more.
“Of course, I did not get off the hot start today I wanted but there is a mid-60s round out there and that is very possible, very possible and if was to win a couple of these you could still walk away with the trophy and a little bit of money, as well.
“It was really a day when I never really got going and that is how it has been the last few weeks as it has felt a little disjointed.”
In contrast, Justin Rose was pleased with his decision to change all the shafts in his irons in recording a two-under 68 and head to the clubhouse sharing seventh place.
“I have not been getting off to a good start the last month or so, so that was a lot more positive,” said Rose.
“I hit my irons as good as I have hit them all year today and that was changing the shafts and back to the shafts I used back in ’14 and ’15 so that was the key today.”
American Russell Henley enjoyed the first round lead with a first new tournament course record six-under 64 and one shot fewer than World No. 1 Dustin Johnson who managed six birdies in a five-under 65.