PORTRUSH, Northern Ireland — It’s been a month since J.J. Spaun experienced the pinnacle of his golfing career at Oakmont, yet he still finds it hard to grasp that he’s the current U.S. Open champion.

“Winning was an incredibly surreal experience,” he shared on Wednesday, ahead of the British Open’s first round at Portrush. “Every morning, I wake up, look at the trophy and have to remind myself that it’s actually mine.”

When Spaun talks so candidly and modestly about his belief in himself, it’s tempting to question whether he thinks he could take a short drive from Portrush to Portstewart—a nearby top-tier links course—and defeat a group of 10-handicap golfers in a match.

“I feel like I’ve had to prove to myself that I’m worthy of just playing on the PGA Tour and winning on the PGA Tour,’’ Spaun said. “It’s hard enough to win in general on the PGA Tour, and you kind of get in your head thinking, ‘Well, if I can’t win a normal event on the PGA Tour, what makes you think you can win a major?’

“I never thought I would win a major. A few years ago, I was just trying to get in them. That’s kind of how my career has developed. I don’t really know what’s in store for myself. I don’t know what I’m capable of now. I know what I can do, and that’s all I can really rely on.’’

What he did in June was seize the moment when the moment was biggest, burying a birdie bomb of a putt on the 72nd hole for a walk-off victory at Oakmont.

Spaun said he “took away a lot of confidence’’ from his U.S. Open triumph.

Now he finds himself grouped with defending champion Xander Schauffele and Jon Rahm in one of the marquee groups for the first two rounds of the 153rd British Open.

“Self-belief is a huge key to pulling off a big event like a major, let alone a U.S. Open,’’ Spaun said. “I hadn’t been in that territory really very often, just once earlier this year at The Players [where he lost in a playoff to Rory McIlroy]. Learning experiences like that have helped me come through on the other side at the U.S. Open.’’

Now Spaun, ranked No. 10 in the world, is a lock to play for the U.S. Ryder Cup team, which seemed unfathomable to him not long ago.

“I don’t think I’ve ever thought of myself in the Ryder Cup,’’ Spaun said. “But I’ve been hearing that a lot throughout the last few years, from my caddie [Mark Carens] and my coach, like they’ve been kind of putting that out there and almost in a way manifesting it, which is kind of weird.

“My caddie always believed in me. Even when I was ranked outside the top 100, he’s like, ‘I think you’re a top 10 player in the world.’ He thinks I could be No. 1, but honestly, let’s be real. But here we are top 10 in the world.”“He always believed I could be on the Ryder Cup, and here we are looking pretty good for the Ryder Cup. It’s just weird how you kind of hear [and] you soak in those things that people tell you, and then it just sort of ends up happening. I think that has to do a lot with developing and believing it yourself.