He's also the seventh straight first-time major champion in men's golf.
"I know I didn't play well, but it was a beatdown I needed so that I learn how to play the game differently and learn what I need to do to become better".
"I've played 25 of them, and if I play another great".
Unfazed Sunday by this distinctive course's amber waves of angst, Koepka, 27, would seem to be of an age and a skill set to make himself far more famous in his chosen field. The average score in the fourth round was 73.9. It wasn't almost enough to catch Koepka, but it earned Matsuyama a tie for second place with Harman.
"Obviously, that's just one shot, but that was a pretty big turn", Thomas said of the bogey on No. 4.
He did it. Now, his journey includes a victory in Wisconsin - in the U.S. Open, no less.
Graeme McDowell, also from Portrush, won the US Open 2010 with Rory McIlroy triumphing the following year. Harman said, "I can't take anything away from how well he played", and, "You've got to tip your cap; he won the golf tournament on the back nine", and, "If you'd have told me I was going to shoot 12 under in the U.S. Open and not win, I'd have taken that bet, that's for sure".
The others included recent Wells Fargo victor Brian Harman, who led Koepka by one as Sunday began and spent the back nine anywhere from 13 under to 11 under before settling at 12 under.
Emotion? The most he displayed was a light fist pump, his hand clenched a little tighter with each birdie, and a double fist pump on the 18th when he tapped in for par.
Brooks Koepka was not a household name on Saturday, but by Sunday night he jumped to golf's upper stratosphere by winning the 117th U.S. Open at Erin Hills. "Not your typical U.S. Open setup, but I'm a big fan".
"To go over there, I think it helped me grow up a little bit and really figure out that, hey, play golf, get it done, and then you can really take this somewhere".
Koepka went to Europe and filled his passport on the Challenge Tour with stamps from Kazakhstan to Kenya, Scotland and Spain, India and the Madeira Island.
SEE YA NEXT YEAR: Qualifiers Xander Schauffele and Trey Mullinax finished in the top 10 and get an automatic entry into next year's U.S. Open.
Harman's chances ended with two straight bogeys, and a bogey on the par-5 18th hole gave him a 72. With Dustin Johnson, Rory McIlroy and Jason Day failing to make the cut, the list of contenders was filled with players looking to become the seventh straight first-time major victor. "I knew after two shots alongside him that this guy was going to be really good", says Elliott. "Brooks dealt with it amazingly - he came and kicked everybody's (butt) over there, didn't he?" He came and kicked everyone's [behind] over there, didn't he?
However, a 72 narrowed his lead before a final round 69 proved good enough for a very comfortable victory, finishing a full eight shots clear of his nearest rivals. "Now he's done it in a major".
Brooks Koepka won the U.S. Open in historic fashion.
"I felt like this was the lowest I could have shot", he said of his disappointing score. Only six players had ever reached at least 10 under par in the previous 116 times at the U.S. Open. McIlroy and Tiger Woods (12 under at Pebble Beach in 2000) had been the only players to finish there.
Four other players are tied for 10th on seven under. He posted a 66 to move to 12 under par, and that left him one stroke behind Koepka at the time he finished his round.
Justin Thomas was unable to sustain momentum after carding a 9-under 63 Saturday, the best round in relation to par at a U.S. Open.
The golfers had their way with Erin Hills for four days, which is unusual for a U.S. Open, where hard courses and diabolical setups by the USGA traditionally make pars, not birdies, the objective.
Koepka cruises to win US Open, first major
The deadlock was broken when Harman's tee-shot on the 12th landed into the deep fescue, forcing him to hack out onto the fairway. Champ had a putt on the 18th hole to tie the 20-year-old but couldn't convert, giving Scheffler the low-amateur honors.
ISIL has claimed responsibility for the attack in Australia
He said it was too early to know what Khayre had been planning, but said it was a "possibility" that he wanted to ambush police. The woman escaped safely but three officers were injured as police stormed the building to end the hostage situation.
Long road: Koepka's journey now includes a US Open title
The 28-year-old remained upbeat despite disappointment, putting it down to a lack of competitive golf this season. But I think what was underestimated was how well he knew me, how well he knew my game. "I've no real concerns".
Harman, Koepka set pace in US Open finale
Justin Thomas was unable to sustain momentum after carding a 9-under 63 Saturday, the best round in relation to par at a U.S. After his winner's press conference Sunday, Koepka exited a back door, carrying the trophy, accompanied by Blake Smith.