Koepka, who became the seventh straight first-time victor of a major, finished the tournament strong, closing with three straight birdies on the back nine and shooting a 5-under 67.
The long-hitting Florida native travelled far and wide, from Kazakhstan to Kenya and mainland Europe, cramming into bed and breakfast rooms with fellow players, spending some nights sleeping in cars, and learning about life and how to win.
"Going over to play the Challenge Tour was really cool", he said after a final round 67 took him to 16-under par for the week and four clear of runners-up Hideki Matsuyama and Brian Harman.
"I don't think I've got that much of an edge because I've not played the golf course enough", said Everton fan Fleetwood, who got his hands on the Claret Jug at Goodison Park in April at a promotional event. He joins Paul Azinger (1993 PGA Championship), Hubert Green (1977 U.S. Open and 1985 PGA Championship) and Jeff Sluman (1988 PGA Tournament) has those former Noles who have bought home major titles.
While now based back in the United States on the PGA Tour, where he has won twice with victories at the 2015 Phoenix Open and now the 2017 US Open, Koepka admits playing golf on the Challenge Tour and European Tour was key to making him the player he is today.
Hisako Higuchi, victor of the LPGA Championship in 1977, remains the only Japanese golfer to win a major championship on either the PGA or LPGA tours.
"It bites a little bit right now", Harman said afterwards. I was just exhausted of golf.
"It hasn't sunk in, obviously, yet, and probably won't for a few days", said Koepka. "And I just couldn't stand the fact that I only won once".
"You know, walking up to the golf ball, I felt like every shot I was going to hit was going to be really good. Not many people get the chance to play a major or even a tournament where they've grown up so it's special for me". "I think that's been the consensus from everyone", Spieth said Sunday.
He followed with birdies at 15 and 16 to suddenly widen his gap to four shots and close in on theOpen championship.
Then in March he secured more than $1 million when he came second in the World Golf Championship in Mexico in March.
"Dustin actually called me last night and told me the same thing, "Just stay patient".
Despite his worldwide success, Koepka had viewed himself as an underachiever, failing to capitalise on opportunities and not adding to his list of titles since that victory in Arizona over two years ago.
He remembers taking a phone call and receiving the best advice he's ever got: "Stick it out".
Hard to think it would've bothered Koepka, who has seen a lot.
As did his globe-trotting apprenticeship as a pro. And some of the places we went to were pretty neat. Like I said, birdied the first. The next year, he earned a spot in the U.S. Open through a qualifier in England, and his tie for fourth at Pinehurst No. 2 helped him earn a card on the PGA Tour. You look back at all the wins, even on the Challenge Tour. "I just tried to keep the hammer down and go as low as I could".