What do you do when you've been in a serious vehicle accident as a child and your doctor advises you to avoid all contact sports?
Koepka, South Korea's Kim Si-woo, Japan's Hideki Matusyama, Englishman Tommy Fleetwood and Americans Brian Harman and Rickie Fowler were the names battling for major glory on Sunday, rather than the likes of Jim Furyk, Stewart Cink and Ernie Els.
The fast-moving Koepka captured the 2015 Waste Management Phoenix Open but despite often putting himself in contention, the wins did not continue to flow and from 21 top-10 finishes on the USA -based tour, he only had the one victory.
"I felt on Saturday I played great". "We stuck with golf for a little while and it's panned out. And I think it was the night of the third round", Koepka revealed.
A fourth place finish at the 2014 US Open had given Koepka a taste of what it might be like to challenge for a major.
Unusually, the finale will not feature any of the world's top three players.
"It's pretty cool", Koepka said after clinching a $2.8 million winner's cheque and the famous US Open trophy.
It was an experience that taught him as much about life as it did about the sport, and the young American went as far afield as Kenya and Kazakhstan as he cut his teeth and honed his game.
"And I felt confident all week, so to feel as confident as I did on a Sunday of a major and coming down the stretch was pretty neat".
The week concluded with 31 players under par, breaking the tournament's record of 28 that happened at Medinah in 1990, and the 133 subpar rounds this year were nine more than the previous high at that 1990 Open. "I just felt like I should be winning more". Here if you played some solid golf and hit your shots where you needed to, you still needed to be precise but you got rewarded and you could take advantage of that. "Jesus came down and said, 'Hey, Marshall, I'm going to bring you up and reunite you with your wife".
But Koepka would not be blown off course producing a near-flawless final round, subduing the winds with a mix of power and precision.
With guys like Jordan Spieth, Rory McIlroy, Rickie Fowler, Phil Mickelson, Day, Johnson, Garcia and many others, the star power on the PGA Tour is at an all-time high making it hard to give Koepka the coverage he deserves. "I played six, probably seven weeks in a row. not being home". I think it helped me grow up a little bit and really figure out that, hey, play golf, get it done, and then you can really take this somewhere.
"They told me to do what I had to do", he said. It's something I do. Tight fairways, diabolically thick rough, and nightmarish greens have been replaced by ever-changing hole yardages, 100 different tee boxes, and a game of chess against USGA executive director and course set-up czar Mike Davis. What's more, his mother, Denise, was fighting breast cancer at the time.
"Did you see that fist pump there on 18", Koepka said with a proud smile.
"It was a long phone call for us, it was like two minutes".
It has all led to this.
"He told me 'Just stay patient".
Johnson might be a man of few words -- with this year's champion joking the resultant two-minute conversation was among the longest they'd ever had -- but the advice has paid off.
"I'd love to get a map and just look at all the places I've won", Koepka said. "I was always very confident, very in control of my game [and] in control of the way I was thinking". And all of those things put together makes him a great caddie for me.
Fleetwood accepts that there will be so much more expectation on him now, with not just his family and friends being there in support.
Brooks Koepka reacts on the 18th hole during the fourth round of the U.S. Open golf tournament Sunday, June 18, 2017, at Erin Hills in Erin, Wis.
After often commenting he feels like "an underachiever", Koepka climbs from 22nd to the top 10 in the PGA rankings.