AUGUSTA, Ga. — It’s on.

Rory McIlroy’s Masters title defense at this year’s 90th edition at Augusta National is off and running — emphatically.

McIlroy probably couldn’t have asked for more out of his first tournament round at Augusta since he captured his initial green jacket last year to complete the career Grand Slam, ending a 14-year drought without a major.

He opened with a 5-under-par 67 and has a share of the lead with Sam Burns entering Friday’s second round.

It was the second-best first-round score of his career, bested only by the 65 he shot in 2011. It, too, was just the third opening round in the 60s in McIlroy’s 18 Masters starts.

“The thing for me over the last 10 years was, I was chasing not only my first Masters, but also trying to win the Grand Slam,’’ McIlroy said. “When I teed it up on the first hole today, I was anxious just like I always am on that first tee. It’s the first round of major season, the first round of the 16 most important rounds of the year.

“I’m thankful that I felt the same as I always have. I think it would be worrisome if I didn’t feel that way because it definitely still means something to me.’’

Only three players in Masters history have won back-to-back green jackets — Jack Nicklaus in 1965-66, Nick Faldo in 1989-90 and Tiger Woods in 2001-02.

McIlroy is well aware of that history and has his eyes on becoming the fourth on that list. But it’s not the borderline obsession winning the first green jacket became after all those years of trying unsuccessfully.

“I think winning a Masters makes it easier to win your second one,’’ McIlroy said. “There are still shots out there that you feel a little bit tight with, and you just have to stand up and commit to making a good swing and not worry about really where it goes.

“But it’s easier for me to make those swings and not worry about where it goes when I know that I can go to the champions locker room and put my green jacket on and have a Coke Zero at the end of the day.

“I still have high expectations of myself, but my expectations are more like, ‘Did I make good decisions today? Was I committed? Was I trusting?’ [But] it wasn’t my expectation of, ‘I’m going to go out and shoot 65 and did I do it?’ ’’

McIlroy played his first seven holes in even par and jump-started the round on the par-5 eighth hole, where he hit a great 3-wood punch approach shot out of the rough and onto the green to make birdie. He would go on to birdie Nos. 9, 13, 14 and 15 on his way home.

“My hope was to get off to a solid start,’’ he said. “I feel like the way I played, 5-under sort of exceeded where I thought I would be or what I wanted to do. I think a fair score for me today would have been like 2-under, maybe, with some of the places I hit it.

“I’m proud of how I scored today when I didn’t really drive the ball particularly well on the front nine. But I was able to scramble and make some pars. From the eighth hole on, I played the last 11 holes in 5-under par.

“I’m proud of how I hung in there in the first few holes when I didn’t quite have it and it was nice to see a few birdies later in the round.’’

McIlroy is tied with Burns, whose 67 was his lowest round at the Masters.

Jason Day, Patrick Reed and Kurt Kitayama all are two shots back at 3-under.

World No. 1 Scottie Scheffler, vying to win the green jacket for the third time in five years, is lurking just three shots back, as are Xander Schauffele and Shane Lowry, all world-class players.

For McIlroy, he’d exuded a vibe of sheer comfort all week, and that comes with knowing you’re a Masters champion forever, with his own space in the champions locker room.

“Sometimes I still have to catch myself and am like, ‘Yeah, I do get to come back here every year.’ It’s such a thrill to be up there with all the other champions. I’ll probably go up there now, have a little drink, put my green jacket on and call it a day.’’

Now that’s what you’d term “proper flex.”