Shane Lowry could not hide his disappointment after surrendering a four-stroke lead at the U.S. Open, though he believes he is good enough to eventually break through and win a major.

Lowry was clear atop the leaderboard when the fourth round teed off on Sunday but his advantage quickly evaporated as American Dustin Johnson claimed his first major title with a three-stroke victory at Oakmont Country Club.

The Irishman faltered dramatically on day four after posting a six-over-par 76, which included seven bogeys, three of those in succession starting at the 14th hole.

In his post-tournament news conference, Lowry told reporters: "Bitterly disappointed, standing here. And, you know, it's not easy to get yourself in a position I got myself in today. It was there for the taking and I didn't take it," Lowry said.

"But you can only learn from your mistakes, I always say it's only a mistake if you don't learn from it. I'm sure I learned a lot from today and I don't know what it is yet, but when I'm in that position again, and I know I will be, I'll handle it probably a little bit better.

"When I look back on this week, there will be a lot of positives to take from it, second place at the U.S. Open, my best ever finish in a major. Good World Ranking points this week.

"Got more ahead for me now, and I feel like I'm hitting form at the right time. Hopefully, I can go back to Bridgestone and make a good show in my defence there. Then I've got obviously The Open and the PGA as well."

Lowry added: "The more I think about it, the more upset I'm getting. It's one of those that's going to be hard to take. It's going to be a tough few days. But I led by four shots in the tournament going into the final round. I had a lead with five holes to play.

"I'm definitely good enough to win one of these. So I'll get back on the horse in a couple of weeks. Back to Firestone in a few weeks."

It was an eventful day in Pennsylvania after Johnson was penalised a stroke by tournament officials.

A penalty was hovering over Johnson with six holes remaining after appearing to cause a ball to move on the fifth hole, though officials did not make a decision until the end of the round, not that it affected Lowry's approach.

"We were told at the 12th [but] it didn't really [affect me]"," Lowry said.

"I actually just lipped out for eagle. Made a great par save on the next, and really thought I was in the tournament. If anything, I was hoping he'd get the one-shot penalty. But that's the way it is. Obviously, he didn't need the extra shot in the end. Of course, it would have been interesting if we were tied at the same score."