“To go back to back, I really can’t even put it into words,” said Koepka, who was flirting with the cut line when he was seven-over par during the second round on Friday.
“We grinded our tail off this week to come back from seven-over and do what we did. It was pretty special.”
The world number nine is the seventh player to win back-to-back US Open crowns, and the first since Curtis Strange in 1988-89.
After overpowering the wide-open Erin Hills, he kept his nerve through four brutal days at Shinnecock.
“It’s much more gratifying the second time,” said Koepka, who had battled a partially torn wrist tendon that sidelined him nearly four months since his major breakthrough last year. “I don’t think I could have dreamed of this.”
A day after scores soared on the dried out greens, the US Golf Association admitted the course got out of hand, adding plenty of moisture and some slightly more forgiving pins.
England’s 12th-ranked Fleetwood seized the opportunity to match the lowest round ever in the US Open with a brilliant seven-under 63 for a two-over total of 282.
Only Koepka met the challenge. He had broken out of the pack with three birdies in the first five holes.
Playing in freshening wind and knowing that Fleetwood was in the clubhouse on two-over Koepka produced a string of clutch putts on the back nine.
A six-foot birdie at the 10th gave him a two-stroke lead. A tough 12-footer limited the damage at 11 to what he called “a great bogey” after he hit over the green into deep rough and from there into a bunker.
He got up and down for par at the 12th, and escaped with a par from deep rough at 14 before giving himself some breathing room with a birdie at the par-five 16th — where he stuck his third shot less than four feet from the pin.
“I felt like I made those clutch eight- to 10-footers that you need to keep the momentum going,” Koepka said. “We didn’t drive it that great, but you can make up so much with a hot putter and that’s kind of what I was doing.”
By the time Koepka’s approach at 18 hit a grandstand and bounced off a closing bogey was academic