"We didn't really speak too much", he added. I don't think it crossed the line, but it was as hard of golf as we can play.
Koepka is among the best of America's new golfers; powerful athletes who, due to their exceptional physical condition, could probably have made a career in any other sport.
The USGA admitted it was at fault on Saturday after several players blasted the course set up at Shinnecock Hills following a day described as "pure carnage" at the US Open. His last victory - and last major - was 10 years ago at Torrey Pines.
"It really, really was testing this week, to be honest with you", Koepka said of the course. "It would have been fun to duel it out with him coming down the end, having to make some putts". I was excited about it. "Hell, I came close, and he'd beat me like a yard dog".
"I made an incredible four", Koepka said. Sometimes the cost of making birdies, sometimes there are some mistakes, which kind of bit me in the butt this week.
Koepka said the two talked about the break of the green on No. 3 but otherwise didn't chat during the round. He finished at 1-over-par 281 for the championship, completing the first successful U.S. Open title defense since Curtis Strange in 1989.
"But that's the way it's supposed to be", he said. "It feels so good to have this thing (the trophy) back in my hands". Today is proof you never know what this game is going to bring around.
Koepka now has two major championship wins before his buddy Dustin Johnson, who reclaimed the number one world ranking after a win last week at the FedEx St. Jude Classic. No one had taken a four-stroke lead into the weekend and failed to win since Tom McNamara suffered a heat stroke on the 68th hole in 1909.
Fleetwood had three good birdie looks on the final three holes that could have yielded him the all-time low score.
Fleetwood began the final day six shots off the lead and finished his round more than two and a half hours before the victor, although the lengthy wait was made more bearable in the company of his baby son Frankie and wife Clare.
Johnson was in the mix most of the day Sunday, amid a tightly bunched leaderboard, but succumbed to three bogeys on the back nine as Koepka held on for history. He nailed putts as long as 57 feet on No. 2 - a great way to get started - and almost 30 feet on the 15th for his final birdie. "I just keep doing what I'm doing, keep plugging away", said Koepka, who despite his defending champion status was flying under the radar at Shinnecock Hills, where Tiger Woods, Phil Mickelson, world number one Dustin Johnson, and multiple-time Major victor Rory McIlroy were generating pre-tournament buzz. Mickelson, who was assessed a two-stroke penalty but not disqualified for the violation, did not speak to reporters after his round.
The Englishman, who also coaches the likes of Henrik Stenson and Matt Fitzpatrick, issued another challenge to ensure Koepka was fully motivated ahead of his latest triumph.