Koepka is trying for his first major championship. He made good pars at the first two holes after shaky drives, birdied the third and turned in a 1-under-par 35. He came into the U.S. Open with one Ryder Cup appearance under his belt, and three top-five finishes in majors. It left him with four strokes to spare over runners-up Brian Harman and Japan's Hideki Matsuyama, with Tommy Fleetwood a shot further back alone in fourth.
"It feels wonderful to get my name on this trophy with so many other great names", Koepka said after becoming the seventh first-time major victor in succession, a run stretching back to Jason Day's victory in the 2015 US PGA Championship.
Those are two of the biggest names in the sport.
The 27-year-old American didn't realize, however, just how close he was to making history. "But, at the same time, I don't feel like I lost a golf tournament, I think Brooks went out and won the tournament".
Instead, he took off for Europe in 2013. That score would have won all but two of the previous 116 renditions of this championship.
"Not a lot (of Americans) do it". "Obviously, Brooks dealt with it amazingly".
"If you had told me I was going to shoot 12-under this year at the U.S. Open and not win, I would have taken that bet for sure, " Harman said.More news: UK's May confident on power-saving deal
If any doubt remained over who was going to succeed Dustin Johnson as the victor of the year's second major, Koepka ensured his victory was inevitable by rolling in yet another birdie on the par-three 16th.
And that is something with which he's scuffled. I suppose I did most things well all week and could be standing here in a different scenario, a different position, if I just had of got a few breaks and maybe holed some putts along the way.
After three days of benign conditions which have led to a feast of low-scoring, the arrival of strong gusts at Erin Hills suggested the challenging course could finally bare its teeth on Sunday.
"He'd been knocking on the door for a while", said Justin Thomas, a two-time PGA Tour victor in 2016 who was in the final pairing.
"To get the calls and text messages I did last night was pretty special". It lasted only a couple of minutes.
"Good job", his wife, Kelly, said as she greeted her husband with a kiss.
Heading into the 12th hole, Harman and Koepka were tied at 13-under. He drilled it in.More news: Penguins return home as betting favourites for Game 5
Showing steady nerves, long hitting and clutch putting, Brooks Koepka pulled away from the pack by posting consecutive birdies on the 14th, 15th and 16th holes on his way to a 5-under-par 67.
And he kept building on that. "Into the wind ... that was pretty impressive".
The champion started the event with birdies on the first and second holes, and if he had any semblance of nerves, they disappeared immediately.
That is about as emotional as he gets.
Not surprisingly, Koepka also wants to see another Open at Erin Hills. Thirty-one players finished under-par, a new tournament mark. Casey, who had shot a six-under-par 66 on Thursday, came unstuck with a disastrous triple bogey eight on the 14th after teeing off on the 10th hole.
And for the week, there were 140 sub-par rounds recorded - with 122 coming in the first three rounds.More news: S.Korean President vows to scrap plans for n-reactors
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