Koepka claimed his fourth major title in his last eight starts by successfully defending his US PGA Championship title at Bethpage after almost letting a record seven-shot lead slip from his grasp.
The 29-year-old American ranked only 44th in driving accuracy over the four rounds, but was third in driving distance and used his enormous power to get himself out of trouble when he tangled with the course’s fearsome rough.
“If these are the golf courses that the PGA and USGA are going to continue to use it’s playing into the hands of 10 guys,” said Sheffield’s Willett.
“Mentally you can be as good as you like but if you don’t hit it 330 yards you’re going to be a long way behind the eight-ball.
“We hit a great one down the first on Saturday and you go online afterwards and see people hitting it much further and think, ‘Huh, it’s a little bit easier from there’.
“But that’s just how it is, that’s the attributes that Brooks has got. You’ve still got to hit it straight and he does.
“He’s turning himself into an unbelievably good player in big tournaments because the set-up of the big tournaments is right where he likes it. He now has nothing to prove to anybody so he’s in a pretty comfortable place.”
Willett has known Koepka since he played on the European Tour after graduating from the Challenge Tour, and even treated the new world No 1 to a night out in South Yorkshire.
“My caddie Sam (Haywood) caddied for Pete (Uihlein) when he and Brooks were hanging round together and we spent a good bit of time together,” added Willett, who finished 15 shots adrift of the winner after he followed Saturday’s third-round 69 with a final round 77 that left him on 287.
“Brooks came for a night out in Sheffield – we took him to some terrible establishments and he stayed at the Jury’s Inn with Sam.”
Koepka admitted he was “emotionally spent” after surviving an unexpectedly nerve-racking final round.
Koepka had followed a course record of 63 on Thursday with a 65 to set the lowest halfway total in major championship history and took a tournament-record seven-shot lead into the last day at a blustery Bethpage.
No player has ever surrendered such a lead in a major after 54 holes and he remained six clear with eight to play, but bogeyed the next four holes to allow good friend and former US Open champion Dustin Johnson to close within a single shot.
However, with the raucous New York crowd chanting his name, Johnson dropped shots on the 16th and 17th to give Koepka the breathing space he so desperately needed and a closing 74 – the highest final round by a major winner in 15 years – was good enough for a two-shot victory.
England’s Matt Wallace was four shots further back in a share of third place with Americans Jordan Spieth and Patrick Cantlay, with Irishmen Rory McIlroy and Shane Lowry among a tie for eighth on one over.
“This one’s definitely at the top of the list in how emotionally spent I am,” said Koepka.
“I’m just glad we didn’t have to play any more holes, that was a stressful round of golf.
“The wind was up, DJ (Johnson) played awesome and he put the pressure on. I’m glad to have this thing (the Wanamaker Trophy) back in my hands.
“It’s incredible. I don’t even know if I dreamed of this. This is cool. I am still in shock right now, this is awesome.”
Koepka replaced Johnson as world No 1 and with the US PGA moving from August to May this year he is the first player to hold back-to-back titles in two majors at the same time following his US Open wins in 2017 and 2018.
Wallace followed his runners-up finish in the British Masters with his best finish in a major and said: “I really dug deep and showed another side to myself, that I was proud and kept churning away and trying to produce the best I could, and two over was the best I could have done.
“That’s what you need to do in majors. So I’ve done it now and hope I can go two steps better in a few weeks’ time (at the US Open).”