Koepka stayed calm and persevered under intense pressure as Woods electrified spectators by displaying the form that made him a 14-time major champion.
The two then shared a brief hug before Koepka continued his way to sign his scorecard.
Four years and two days after his last major victory at Valhalla, McIlroy carded a final round of 70 at Bellerive Country Club to finish two under par for the final major of the year.
The atmosphere around the course was electric, the bumper crowd caught up in another vintage PGA Championship performance.
Brooks Koepka has defended his US Open.
Scott needed a special invitation to get into the PGA Championship.
"I'm pretty disappointed with myself that I couldn't play the last three holes better than I did", Scott said. I warmed up hitting it left, I was hitting it right with every single club, even my sand wedge I wasn't doing very good. Its soft, it's gettable and you can't just go out there and make a bunch of pars. 14 and 16 en route to a Sunday 68 and a tie for sixth at 10 under par. Thomas turned birdie into bogey at the turn with a three-putt from 5 feet, and he missed a short par putt on the 14th to fall back.
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The damage inflicted by President Trump's naivete, egotism, false equivalence, and sympathy for autocrats is hard to calculate". The witch hunt he refers to is the allegations of Russian meddling in the presidential elections which put Mr Trump in office.
As Woods made his move, the crowd certainly let the on-course leader know with an ever increasing volume of sound that greeted nearly every shot, reaching a crescendo when Woods birdied the final hole.
Woods saves par on the 17th after a terrible start to his penultimate hole. Koepka now with a chance for the outright lead. He finished with six birdies and two bogeys in the final round.
"As much as I can", Brown said of trying to follow Woods throughout his round. I've kind of had some trouble with that over the past two or three years. "So that takes far more precedence than me playing a major". He also got robbed on No. 11 after leaving a birdie putt hanging on the edge of the cup. It failed him all day Saturday, when he could not convert birdie putts to close his second round and throughout his third round during a 29-hole day in the St. Louis heat.
As Thomas faded, Scott and Woods charged at him, but Koepka remained steady.
Woods, searching for a first major win since the 2008 US Open, moved into contention after a blistering front nine which contained five birdies and one bogey.
"I played hard", Woods told CBS Sports. "I made a bit of a run".
"A couple years have slipped by where I really haven't contended and I'm going to relish it tomorrow because if it's another five, basically you're wheeling me out to pasture at that point", he said after the best round of the afternoon. "I had the lead there". I was always trailing. "I had to keep making birdies".
Woods broke with his own convention by waiting to warmly congratulate Koepka as the champion walked from the course. "You want guys that have had a good solid season".
Brooks Koepka holds off Tiger Woods, Adam Scott to win PGA Championship
The four-time PGA Championship victor made five birdies and one bogey through eight holes and finished with 10 consecutive pars. Fleetwood signed off with a 68 for tied 36th place. "It's been a pleasure to play in front of them, it really has", Woods said.
For Woods, it was the lowest score in the final round in a major in his career. "When Tiger started making his little run, and Scotty made his run, it got loud".
It's not just the American players who are digging the atmosphere.
Woodland is second to Brooks Koepka (1.59) in the tournament in strokes gained off the tee (1.255).
"A lot of frustration, honestly", he said.
"I just need to figure out Augusta; I haven't quite had the results there I've had elsewhere". "So that's a bummer".
Woods finished in style with a birdie on the last for a 64 to match the day's best round with Spain's Rafa Cabrera Bello and Englishman Tyrrell Haton.
Three-time major victor Jordan Spieth finished in a tie for 12th at 8 under after a 66 on Sunday.
Sunday's play will decide the victor of the fourth and final major of the golfing season with the PGA Championship itself moving to a May date for the 2019 season.
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And the longer-term loss of markets for American crops is far worse that the short-term financial hit, he said. Juncker also agreed to buy billions of dollars more in USA soybeans and natural gas.
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