Koepka won by one shot over England's Tommy Fleetwood with first, second, and third round co-leader Dustin Johnson another shot back.
His final round of 68 was not the lowest round of the day but it was perhaps the best and the most important as it came at a time when it was needed most and separated the 28 year old from the world’s best and presented him with his second consecutive US Open title.
In doing so, Koepka became the first player to win consecutive US Open since countryman Curtis Strange in 1988 and 1989.
Koepka made the perfect start after heading into the final round tied with Dustin Johnson, Daniel Berger and Tony Finau, making three birdies in his first five holes to move clear of the field.
His nearest challenger at that point was a red-hot Patrick Reed who had birdied five of his first seven holes to join Koepka in the lead at 1 over after Koepka bogeyed the 6th.
A three-putt bogey by Reed at the 9th handed Koepka the outright lead and from that point on Koepka led, extending the margin to two when he birdied the 10th although by then it was Johnson and England’s Tommy Fleetwood who were his closest challengers.
Fleetwood had finished over two and a half hours earlier, equalling the best ever round in US Open Championship history with a round of 63 but will rue a missed opportunity from 9 feet at the last which broke a little more then he anticipated.
A brilliant bogey at the 11th hole by Koepka after missing the green left then right kept him one ahead of Fleetwood after Johnson three putted and another birdie at the 16th after a stunning pitch from 120 yards set up a two-shot lead.
While the final two holes presented their own dangers he was able to par the 17th and bogey the last to win by one.
That Koepka was able to keep his nose in front despite the demands of Shinnecock Hills and join an elite club of back-to-back US Open winners further highlights his rapid elevation at the elite level.
Koepka will move inside the world top 5 as a result of his win, his previous best being 7th late in 2017 while Fleetwood will move inside the top ten for the first time in his career from his current 12th place.
"The U.S. Open just takes so much discipline," said the champion. "You have got to be a great putter and just kind of let things roll off your back. That is something we do pretty well.
"We were able to bounce back very well considering whether it be a bogey, a double and just kind of move on. It's a fun week. I enjoy the test. I enjoy being pushed to the limit. Sometimes you feel like you are about to break mentally, but that's what I enjoy. I enjoy hard golf courses. I enjoy playing about the toughest in golf you are ever going to play."
Still not yet able to comprehend his achievement Koepka was at a loss for words when trying to describe the moment.
"It sounds incredible. To be honest with you, probably couldn't have dreamed of it in my wildest dreams. I'm at a loss for words right now, but it's really incredible. I mean, I couldn't be happier. We grinded our tail off this week to come back from 7-over and do what we did. It was pretty special."
Fleetwood had a lengthy wait to determine whether he may or may not be involved in the final outcome of the event. While doing so he spoke to the media.
Tommy Fleetwood acknowledges the crowd after his stunning final round (Photo courtesy of USGA).
"Well, I honestly never really thought I was out of it, he started when referring to his round of 78 yesterday which appeared to the outsider that it may have cost him any chance. "I just needed a good start. You never know what's going to happen.
"And obviously, we knew they would have made it a bit softer today. Looking at the pins, you knew they were going to be more accessible. I knew I was kind of in it teeing off, but you still have to get off to that good start. Four under through seven, and it was game on.
"All the way around, I always felt like I could get myself back in it. It's funny, though, when you finish, you always feel like you've kind of missed your shot, but we'll see."
As it turned out he was right - he missed by one but his career continues its own meteoric rise.
World No. 1 Johnson had a horror day on the greens with 34 putts and opted not to talk to the media.
Another story of the final day was the perfect set-up of the golf course after Saturday had eaten away at the credibility of the USGA. They got it right today with a golf course that rewarded quality play and punished anything less.
Shinnecock Hill’s integrity and the event’s reputation was restored by what appeared to be the perfect test of skill and nerve.
Aaron Baddeley headed the Australians in a share of 25th and more information on the Australasians can be found here.
SIGNATURE HOLES: 13TH AT BROOKWATER (QLD)
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