McIlroy shot a three-under-par 67 to open the BMW Championship, taking a share of the overnight lead.
The world number one carded five birdies before two late bogeys marked his card, but it was his up-and-down on the par-four fifth that he claimed was one of his best in 2014.
"It was a brutal lie, and I was just trying to get it somewhere on the green," the Northern Irishman said.
"But when it came out, it came out really well and landed pretty much perfect and ran down there.
"I was just really making sure I was going to hole the putt, because it was probably the best up-and-down I've had all year."
McIlroy compared the course at the Cherry Hills Country Club to that of a US Open venue.
The comparison bodes well for Martin Kaymer, who is tied for fourth after Thursday's play - but won the US Open by eight strokes at Pinehurst.
"I felt like I was going nicely, and even though I bogeyed a couple of holes coming in, that the scoring isn't that good out there," McIlroy said.
"Not that it's not that good, it's just not that low. It's tricky. The greens are firm.
"It's playing a little bit like a US Open. I wouldn't say it's quite as difficult as that, but it's thick rough, especially around the greens, and firm greens.
"That's what they need to keep the scoring the way it is."