Koepka's final round at windy, hard Bethpage Black was filled with late bogeys but the powerful American held on to secure his fourth major title in less than two years, smashing records on the way.
Bruce Koepka: Yeah, dump the card, but don't throw out the Wanamaker Trophy, the heaviest reward in golf. Koepka covered the second 36 holes in sixteen more shots compared with those record-breaking early rounds.
Koepka, who earned a winner's cheque of £1.56m and said: "I'm just glad we didn't have to play any more holes".
"That was a stressful round of golf, DJ [Johnson] played awesome".
McDowell played a role in persuading Elliott to take on Koepka and he believes the happy-go-lucky Ulsterman is the flawless foil for the hard-nosed Floridian. "He did a great job putting pressure on me, making me play some solid golf down the stretch". He joins Raymond Floyd (1982 PGA) and Jack Nicklaus (1980 U.S. Open) as the only players to go on to win from that point.
Koepka became the first player since Woods (1999-2001) to win four US-based majors from six starts.
Koepka's instructor, Claude Harmon III, said the blip could work in his favour, adding: "He learned a lot about himself".
"It's incredible. I don't even know if I dreamed of this". He's the fifth wire-to-wire victor in the PGA Championship.
What had seemed for much of the tournament to be a coronation nearly became a calamity on Sunday, to the delight of most of the raucous NY gallery, who were openly cheering against Koepka as he walked off the 14th green with a tenuous one-stroke lead.
That was as close as Johnson got.
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Johnson, who shot 69, shrank the margin to four shots at the turn and just one with four holes to play, only for Koepka to outlast his U.S. compatriot.
His seven-shot lead through 54 holes was the largest in PGA Championship history.
"But I'm pleased with where the game's at".
"He's one of the guys that I look for that I have to beat", Johnson said.
When his 6-foot par putt fell on the last hole, Koepka thrust his muscular right arm in the air and hugged his caddie hard. Moments after Koepka's bogey streak reached four holes, Johnson gave a stroke back with a bogey at No. 16 and then another on the next hole, when he missed the green on the par-3 17th.
Koepka is a devoted practitioner of tunnel-vision, but certainly he had to be aware of the onrushing train that was Dustin Johnson, and the crowd rolling with him. Up ahead, the Johnson surge had run out of steam, especially when he hit his second shot over the No. 16 green that led to a bogey. I've been to sporting events in NY, I know how it goes.
It gave Koepka a little more breathing room, and even with a three-putt bogey on 17 the defending champion stood on the 18 tee with a two shot lead.
"I knew I needed to do something on the last three holes", Johnson said. "I just didn't play well enough". "I'm not focused on anything else other than hitting a good shot or a good putt".
Koepka shot a four-over-par 74 to finish at eight-under 272 and captured his fourth major title in his last eight starts in grand slam events.