Shane Lowry shakes hands with Andrew Landry at the end of their round during the final round of the 2016 U.S. Open at Oakmont Country Club in Oakmont, Pa. on Sunday, June 19, 2016. (Copyright USGA/Joel Kowsky)

Shane Lowry confessed he was “bitterly disappointed” to blow a four-shot lead but insisted that Dustin Johnson deserved his US Open triumph despite a rules decision delay that took some drama out of the back nine.

The 29-year old from Offaly dropped three shots on the front nine to fall behind, then three-putted the 14th, 15th and 16th and carded a six over 76 to end up tied for second, three behind the eventual champion on one under.

Though he birdied the last and the scoreboard showed a 68 for a four shot win on five under par, Johnson was handed a one-stroke penalty for causing his ball to move at the fifth and signed for a 69 and three shot win on four under 276.

Shane Lowry wipes his eyes as he finished his round during the final round of the 2016 U.S. Open at Oakmont Country Club in Oakmont, Pa. on Sunday, June 19, 2016. (Copyright USGA/Michael Cohen)

“I’m bitterly disappointed, standing here,” Lowry said. “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.

“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.”

Lowry tied for second with Jim Furyk (66) and Scott Piercy (69) on one under par 279 as controversy raged over the USGA’s handling of Johnson’s rules infraction.

The timing of the penalty caused confusion for millions of television viewers and left the players uncertain of exactly where they stood.

Johnson said at the fifth he had not caused his ball to move but officials reviewed video evidence and came back out to tell him at the 12th that they believed he had a case to answer.

Dustin Johnson poses with the trophy after winning the 2016 U.S. Open at Oakmont Country Club in Oakmont, Pa. on Sunday, June 19, 2016. (Copyright USGA/JD Cuban

As Johnson was adamant he was in the right, the officials opted to wait until after the round to discuss it with him in more detail and show him the video and explain their exact interpretation of the rule,

In the end, he was not penalised until after he had finished on the 18th, hitting a stellar approach to five feet and rolling in the putt for birdie.

“We were told walking on 12,” Lowry said when asked at which point he became aware that Johnson might be one shot worse off that the leaderboards suggested.

“No, it didn't affect the way I played. If anything, I credit Dustin for playing the way he played on the way in, having that hanging over him, because I probably would have wanted to know straightaway if it was me. So yeah, that's what we were told.”

hane Lowry on the 13th tee during the final round of the 2016 U.S. Open at Oakmont Country Club in Oakmont, Pa. on Sunday, June 19, 2016. (Copyright USGA/Darren Carroll)

Shane Lowry to his shot at 13th tee going into a bunker during the final round of the 2016 U.S. Open at Oakmont Country Club in Oakmont, Pa. on Sunday, June 19, 2016. (Copyright USGA/Darren Carroll)

It was sad end to a wonderful week for the 29-year old from Offaly, but for Johnson, who three putted the 72nd hole to lose the US Open to Jordan Spieth last year, it was sweet redemption.

His win erased the pain of several major disasters as he holed a nine footer for par at the 16th to remain two ahead, then birdied the 18th thanks to towering 191 yard approach to five feet.

In 2010, he blew a three-shot lead to lose the US Open to Graeme McDowell, then missed out on a three-hole playoff for that year’s US PGA when he was handed a two-stroke penalty for grounding his club in a bunker on the 18th that he believed was just a sandy area.

Two years ago he took the second half of the year off to seek professional help for "personal challenges”.

The controversy of the fifth lingered all night as Johnson was only told by officisals as he walked off the 11th green that he might have a case to answer.

Shane Lowry on the 15th tee during the final round of the 2016 U.S. Open at Oakmont Country Club in Oakmont, Pa. on Sunday, June 19, 2016. (Copyright USGA/Darren Carroll)

The ruling was ironic as Lowry called a penalty stroke on himself on the seventh hole of his second round on Saturday, making bogey at the 16th after he said he had caused the ball to move.

:The Lowry situation was a little bit different because the conversation Lowry had with the referee, he didn't question whether or not he caused the ball to move,” USGA official Thomas Pagel said.

“I talked to the referee, and as I understand the facts, he turned to the referee and said, I caused the ball to move. The question was where do I play it then? Do I play it from its new location, or do I have to play it back?”

Johnson grounded his club to the left of his ball several times and then took some practice stokes before hovering the putter behind the ball.

Shane Lowry saves par on the 13th hole during the final round of the 2016 U.S. Open at Oakmont Country Club in Oakmont, Pa. on Sunday, June 19, 2016. (Copyright USGA/Darren Carroll)

When it moved a second or so later, he called for an official and insisted he had not addressed the ball or caused it to move as he had not grounded his putter.

“They said they were going to look at it when we got done,” said Johnson, who mistakenly believed that he shouldn’t be penalised as he hadn’t addressed the ball.

However, he was eventually penalised by the USGA after a review of the tape as they believed it was more likely than not that his actions around the ball had caused it to move.

Pagel said: “There is a great deal of misunderstanding about the rule which I think has lead to some of the comments [on social media].

Shane Lowry bites his putter after missing a par putt on the 14th hole during the final round of the 2016 U.S. Open at Oakmont Country Club in Oakmont, Pa. on Sunday, June 19, 2016. (Copyright USGA/Darren Carroll)

“We tried to explain it to him but again, in that moment on the 12th tee, he is playing and we are not going to reach a resolution there.”

Pagel added: “I think the one think people need to understand is that by no means are we suggesting that Dustin is a liar. I’ve seen that chat out there and that bothers me.”

Johnson said: “I felt like I wasn't going to be penalised, so I just went about my business. Just focused on the drive on 12 and from there on out, that we'd deal with when we got done.

“It doesn't matter now, and I'm glad it didn't matter because that would have been bad. But, you know, it worked out.”

Lowry completed a third round 65 early in the morning to head into the final round with a four-shot lead over Johnson and Landry, who shot 78 to slip to tied 15th on five over.

Shane Lowry plays his second shot on the fourth hole during the final round of the 2016 U.S. Open at Oakmont Country Club in Oakmont, Pa. on Sunday, June 19, 2016. (Copyright USGA/Darren Carroll)

He looked cool and calm as he headed to the first tee but he turned for home one behind as he bogeyed the second, fifth and ninth.

Johnson birdied the second by driving the green, then birdied the ninth from eight feet to grab a share of the lead with Lowry on five under.

The Clara man then drove into a bunker at the ninth and had to lay up, dropping another shot to head down the stretch three over for the day and a shot behind.

The fifth hole ruling wasn’t the only one to affect Johnson, who began the back nine by hooking into deep rough at the 10th.

Almost unbelievably considering it was hard to find the ball, he got to line of sight relief from a TV tower between him and the flag, and was awarded a free drop at the nearest point of relief from a Temporary Immovable Obstruction, which happened to be in the first cut of rough.

“I didn't get two club lengths (relief),” Johnson explained in reply to a query about the number of clubs lengths normally awarded for a free drop.

“I think they're called temporary, immovable obstructions. Once you can see the flag, then you get a club length from there, and then you drop in the second one. So that's just how the rules say you do it.”

USGA officials explained that Johnson was awarded the correct relief from a TIO, with social media chatter revealing a general lack of understanding of the rules from ordinary fans and tour players.

As he headed down the 12th, Lowry was tied for second with Sergio Garcia and Scott Piercy on three under, two behind Johnson.

Dustin Johnson reacts to his tee shot on the 14th hole during the final round of the 2016 U.S. Open at Oakmont Country Club in Oakmont, Pa. on Sunday, June 19, 2016. (Copyright USGA/JD Cuban)

But with officials telling Johnson they would wait until after the round to speak to him about whether or not he had caused his ball to move on the fifth, Rory McIlroy and Jordan Spieth jumped on Twitter to slam the USGA and defend Johnson.

McIlroy tweeted: “This is ridiculous... No penalty whatsoever for DJ. Let the guy play without this crap in his head. Amateur hour from @USGA.”

Spieth wrote: “Lemme get this straight. DJ doesn't address it. It's ruled that he didn't cause it to move. Now you tell him he may have? Now? This a joke?”

Lowry birdied the 12th to get to within one of Johnson (or tied for the lead depending on the eventual decision) and then got up and down from sand at the 13th, holing a key 10 footer for his par to remain one back.

When Johnson then three-putted the 14th to fall back into a tie for the lead (or one behind, depending on the outcome of the ruling) there was anger that the result might be decided by USGA in an office at the 18th, removing the drama of the race down the stretch.

As it turned out, Lowry’s three consecutive three-putts from the 14th and Johnson’s par save at the 16th and his closing birdie made the eventual penalty irrelevant.

Shane Lowry after making par on the first hole during the final round of the 2016 U.S. Open at Oakmont Country Club in Oakmont, Pa. on Sunday, June 19, 2016. (Copyright USGA/Darren Carroll)

“Had a great number on the 14, just hit a really poor shot,” Lowry said of his 131 yard approach that came up 40 feet short, leading to the first of three, three-putts in a row.

“It, just kind of spiralled out of control from there. It was one of those where I'd give anything to have that wide shot on 14 back again.”

He would save a great par at the 17th after fluffing his chip and also par the last despite his disappointment.

Asked how he felt coming down the stretch, he said: “I tried my best to win this thing. It's difficult to describe the way I felt. My bad holes, I probably got a little bit quick. Everything happened quickly. But, you know, that's what happens when you play a few bad holes. They're kind of over before you know it. You'd like to have them back again.”

Shane Lowry reacts to saving par on the 13th hole during the final round of the 2016 U.S. Open at Oakmont Country Club in Oakmont, Pa. on Sunday, June 19, 2016. (Copyright USGA/Fred Vuich)

USGA rules officials Jeff Hall and Thomas Pagel gave a news conference after the tournament to explain their decision to penalise Johnson for his infraction at the fifth, pointing out that there was a lot of misinformation and confusion of the interpretation of Rule 18-2.

“We said, we'll show it to you when you come in,” Hall said of the decision on the 12th to wait until the 18th to decide Johnson’s fate. “We'd like you to have the benefit of what we have, of what we've seen, so that hopefully he could get more comfortable with the situation.”

Graeme McDowell, meanwhile, did well to finish tied 18th on six over after a 72 considering he made two double bogeys in the first five holes.

“I got off to slow starts both rounds,” McDowell said of his weekend. “If I could have mastered those first eight holes, I'd have had a decent weekend. But all in all, some good stuff there.”

Dustin Johnson poses with the trophy after winning the 2016 U.S. Open at Oakmont Country Club in Oakmont, Pa. on Sunday, June 19, 2016. (Copyright USGA/Jeff Haynes)

Looking forward to pushing for a Ryder Cup place over the next month, he added: “This is a US Open. It's hard. It kind of beat me up a little bit. But definitely taking some good positives out of here.”