The Northern Irishman has won four Major Championships but had carded just 15 opening rounds in the 60s in 52 appearances coming into this week and after his 65 even said it was nice to get off to a good start "for a change".
His round was his lowest opening effort in a Major Championship since a 65 at the 2011 U.S. Open and came after he finished his last Major with a 64 in finishing second at the Masters Tournament.
He carried that momentum into a top-five at the Wells Fargo Championship on the PGA TOUR and was delighted to stay on a roll in Tulsa.
"It was a great start to the tournament," he said. "I've been playing well coming in here. I've been carrying some good form.
"Obviously I took a lot from that last round at Augusta, played well up in DC at the Wells Fargo there, and played good in the practice rounds earlier this week.
"I think when your game is feeling like that, it's just a matter of going out there and really sticking to your game plan, executing as well as you possibly can, and just sort of staying in your own little world. I did that really well today.
"It was nice to get off to that good start and sort of keep it going."
After a pair of opening pars, McIlroy put his approach at the 12th to tap-in range and that sparked a run of scoring that took him clear at the top of the fledgling leaderboard.
I think when your game is feeling like that, it's just a matter of going out there and really sticking to your game plan
He got up and down at the par-five next, holed a 26-foot right-to-lefter on the 14th and then put a shot to nine feet on the 15th to make it four in a row.
A run of four pars was broken by a 14-footer on the second and when he made a smart up-and-down from the sand after getting up by the green in two on the 665-yard fifth, he led by three.
Bogeys were to come as the 33-year-old missed the green at the par-three sixth and eighth but he holed a 19-footer for birdie at the ninth to complete a stunning start.
"I feel like this course, it lets you be pretty aggressive off the tee if you want to be, so I hit quite a lot of drivers out there and took advantage of my length and finished that off with some nice iron play and some nice putting," said McIlroy.
"Sometimes you can maybe start to be a little careful or start to give yourself a little more margin for error but I stuck to my game plan.
"I stayed aggressive, hit that driver up four, took an aggressive line on five. I stuck to what I was trying to do out there, which I was pleased with.
"But it's very easy to make bogeys out here. You get yourself just a little bit out of position, you catch a little bit of grain around the green, it's tricky.
"I didn't encounter too many of those tricky scenarios today but it can certainly be tricky. You get yourself out of position here, you just try to make a four or a par and run to the next."