Amid relentless pandemonium as Woods crept closer, Koepka ran off three straight birdies to end the front nine and seize control at Bellerive Country Club in St. Louis. When he was tied with Adam Scott through 14 holes -- with Woods now just one shot behind -- Koepka delivered back-to-back birdies.
The last one was a laser of a 4-iron from 248 yards that settled 6 feet away, sending him to a dream finish of a year that began with the 28-year-old Floridian wondering if a wrist injury that kept him out four months would ever allow him to compete again.
"That will probably go down as probably one of the best shots I've ever hit under pressure,'' he said.
He closed with a 4-under 66 for a two-shot victory over Woods and took his place among the elite in golf. Koepka became the fifth player to win the U.S. Open and PGA Championship in the same year, joining Woods, Jack Nicklaus, Ben Hogan and Gene Sarazen.
It will be impossible to overlook him now, not with the Wanamaker Trophy to go with his back-to-back U.S. Open titles. Koepka won two of the three majors he played this year, and three of his past six. Not since Woods won four in a row through the 2001 Masters has anyone won majors at such an alarming rate.
And yet it still felt -- and certainly sounded -- as though he played second billing to Woods.
"We knew what was going on,'' he said. "It's pretty obvious when Tiger makes a birdie. Everybody on the golf course cheers for him.''
The crowd was enormous, louder than anything in golf this side of Augusta National or a Ryder Cup, and Woods looked closer than ever to capping his comeback from four back surgeries with another major.
Even with two bogeys, Woods shot 64 for his lowest final-round score in a major. He finished at 266, beating by three shots his best 72-hole score in a major.
But at this major, it wasn't enough.
"I played hard,'' Woods said. "I made a bit of a run. It looks like I'm going to come up a little short.''
Koepka was responsible for that.
After wasting one chance to put it away by missing consecutive birdie chances from 7 feet, Koepka kept attacking flags and ran in birdie putts of 10 feet on No. 15 and 7 feet on No. 16 to end the drama. He tapped in for par on the final hole to set the PGA Championship scoring record at 264. It also tied the major championship record that Henrik Stenson set at Royal Troon two years ago in The Open.
He also joined Jordan Spieth, Woods, Nicklaus and Tom Watson as the only players with three majors before turning 30 since World War II. "Three majors at 28 -- it's a cool feeling,'' said Koepka, who five years ago was toiling in Europe's minor leagues.
Scott hung around by making big putts, just like he hoped, and was tied for the lead until Koepka's birdies. Scott missed a 6-foot birdie putt on the par-5 17th that would have pulled him to within one shot -- right after Koepka missed from the same range -- and then made bogey on the 18th for a 67 to finish alone in third.
The only knock on Koepka is that he doesn't win enough elsewhere -- the Phoenix Open on the PGA Tour, the Turkish Airlines Open on the European Tour, and two victories at the Dunlop Phoenix on the Japan Golf Tour.
"He's won three majors now, so he's definitely winning the right ones,'' Scott said. "If I was him, I wouldn't change much at the moment. I'd just keep doing what he's doing because he's showing up at the right moments in the biggest events. There's something inside his brain that makes him believe that that's what he's destined to do.''
Koepka never imagined a year like this. He missed four months at the start of the year when a partially torn tendon in his left wrist, causing him to sit out the Masters. He outlasted good friend Dustin Johnson at Shinnecock Hills to become the first back-to-back U.S. Open champion in 29 years.
"When I look at what I've done in the past two months it's incredible," Koepka said. "Looking where I was, sitting on my couch watching the Masters, and to think I would do this, I would've laughed at you and told you there was no way, no chance."
And to do it is really incredible. You know my doctors, physios, trainers everybody did an unbelievable job even to get back on the golf course and to do what I've done is very impressive. I can't even believe it."
The only downer for Koepka is having to wait eight months for the Masters.
The Associated Press contributed to this report.