Koepka carded a closing 67 to finish 16 under par, matching the tournament scoring record set by Rory McIlroy at Congressional in 2011.
Only six players had ever reached 10-under par at any point in a U.S. Open in the 116 previous championships. There were 133 sub-par rounds, nine more than the previous record in that 1990 U.S. Open.
"It means I have a lot better chance to win the tournament than I did when the day started". "I come from a baseball family".
Tied for the lead with six holes to play, Koepka holed an 8-foot par putt on the 13th hole that gave him confidence with his stroke and momentum to pour in birdies on the next three holes to turn the final hour into a celebration of another young star in golf. He also extends the streak of first-time major winners to seven.
Tied with Koepka at 13 under, Harman missed his par putt at the par-4 12th to fall a shot off the lead.
Koepka, who looks as if he would be at home in a National Football League huddle, held firm against buffeting winds and crushing pressure to claim a sensational four-shot victory over Harman and Matsuyama. And he said he was pulling for me and just hang in there.
NOTEWORTHY: None of the top 18 players on the leaderboard have won a major. They're all under the age of 30. But I thought it was great.
Schauffele entered the U.S. Open with little acclaim but left with an invitation to the 2018 U.S. Open at Shinnecock Hills by tying for fifth at 10 under.
"Yeah, if you had told me I was going to shoot 12 under this year at a U.S. Open and not win", he said, "I would have taken the bet for sure".
Harman and Koepka spent much of the round locked at the top of the leaderboard.
GRAND RAPIDS, Mich. (AP) - Brooke Henderson won the Meijer LPGA Classic for her fourth LPGA Tour title, holding off Michelle Wie and Lexi Thompson by two strokes in cool and windy conditions. He says he loved seeing different parts of the world, but there was hardship, too.
"That's awesome", Koepka said. Koepka said he phoned his Dallas-based agent, Blake Smith, vice president of Hambric Sports. "No regrets, but I did play well".
"It hasn't sunk in, obviously, yet, and probably won't for a few days", said Koepka.
"I think it's an awesome golf course", Spieth said after his final round.
Smith, the son of Royal Oaks pro emeritus Randy Smith, gave Koepka a pep talk that night.
Cameron Champ was the lowest amateur heading into the final round, but he finished with a 4-over 76 to drop back to even par for the tournament.
Like Koepka, Harman hadn't bogeyed a hole on the back nine until Sunday.
After his winner's press conference Sunday, Koepka exited a back door, carrying the trophy, accompanied by Blake Smith.
The putts and strategy were nice, but on the last, the longest hole on the course, Koepka made a decision to remind us all of that absurd pop he does have.
"Yeah, I don't get those very often".