In an up and down 18 holes at Southern Hills Country Club in Tulsa, Oklahoma, a series of four consecutive birdies for McIlroy on his first nine holes helped propel him to the top of the standings.
But after showing why he is a four-time big winner, the 33-year-old struggled on the back-nine, two bogeys on his 15th and 17th holes dragged him back into the pack and finished at the top of the standings with Will Zalatoris and Tom Hoge.
However, as with the Masters, McIlroy’s round ended in a boom.
He made a birdie putt on his last hole of the day — the par four ninth hole — to make him one clear and close a superb opening in Oklahoma.
McIlroy told media afterwards that it was a “great start to the tournament” for him.
“I played well to get in here. I’ve had good form,” he explained. “Obviously that took a lot from that last round in Augusta, played well in DC at the Wells Fargo there, and played well in the practice rounds earlier this week.
“I think if your game feels like this, it’s just a matter of going out there and really sticking to your game plan, doing the best you can and just staying in your own little world.
“I did a really good job of that today. It was nice to get off to a good start and kind of keep it up. I’m looking forward to this course, it lets you be pretty aggressive off the tee if you want to, so I hit quite a lot of drivers out there and took advantage of my height and ended that with some nice iron play and some nice putts.”
McIlroy was in a blockbuster group alongside Jordan Spieth and Tiger Woods.
Both Americans struggled, however, Spieth carded a two-over 72 and Woods finished with a four-over 74.
For 15-time major winner Woods, it is his second major since returning from a nearly 17-month hiatus due to a serious leg injury sustained in a car accident in February 2021.
Woods said his “leg doesn’t feel as good” as he’d like.
“We will start the recovery process and go after it tomorrow,” he explained.