Koepka's stern demeanour looked unshakeable as he set the lowest 36-hole score in majors to take a seven-shot lead, a margin which remained after the third round when he shot a level-par 70 because his rivals were unable to mount a serious challenge.
But this wasn't strictly business.
Koepka's instructor, Claude Harmon III, said the blip could work in his favour, adding: "He learned a lot about himself". Koepka is the first player to shoot two 63s in the same major, and the first to do so in consecutive years. "To be standing here today with four majors, it's mind-blowing".
Koepka is one of three players in the last 30 years to win three majors before the age of 30.
"I feel confident. I feel good". It's very - it can change very, very quick.
Koepka defends himself given the hard course and windy conditions. You want negative comments?
"Today was a nice way to finish".
"I'm just happy we didn't have to play any more holes", Koepka said after the round. Why would I stray from that? The first came at the Waste Management Phoenix Open in 2015 when he held off Hideki Matsuyama, Ryan Palmer and Bubba Watson to win by one stroke. We knew how firm his resolve.
"Tell you what, the hour spent from number 11 to 14 was interesting", Koepka said. "When they started chanting for DJ on the 14th, it actually helped".
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It was the best thing to happen to Varner on Sunday. He was not quite the preternatural teenage sensation like Woods or Spieth; his first PGA Tour win came at 25, and first major at 27.
"It's New York. What do you expect when you're half-choking it away?" I think I kind of deserved it. I'm feeling a bit bruised and battered but I have to say the game is OK and I'm looking forward to the next few weeks.
"I was right there". I got here Tuesday afternoon and it's been an incredibly long week. Let's go. Yeah, I mean, I definitely heard the cheers, too. I've been to sporting events in NY, I know how it goes. "Kind of all that was going on at the same time". I was just in shock, I think.
We have to go back more than a century to find the only occasion anyone won the US Open three times in-a-row. In high wind, he didn't make a bogey until the 11th hole and shot a 69.
Asked if he anxious that he would fail, Koepka replied: "It was definitely a test. I was trying my butt off", he said.
"I knew I needed to do something on the last three holes", Johnson said. That's all I can do. You've got to find a chip or something to motivate yourself.
"Hit the shot I wanted to right at the flag", Johnson said. "But I never once thought about it". "I don't know how you miss that slope, but I did".
"Good luck to Europe with the fans".
Nothing good happened after that and it seemed Varner just tried to play fast the rest of the way on a very windy, hard day. I hope I'm on the team.
"It's going to take something special to catch Brooks, but it's doable, " Johnson said.