Brooks Koepka has major No. 5 in his sights as he takes the 54-hole lead into the final round of the PGA Championship at Oak Hill

Brooks Koepka began the third round of the PGA Championship being booed by a small but vocal minority of fans surrounding the first tee. He ended it receiving a raucous ovation on the 17th green as the gallery at Oak Hill came to realize a simple fact: Koepka is now the man to beat in Sunday's final round.

Koepka shot a second consecutive round of 66 on Saturday to take the 54-hole lead at six-under, a shot ahead of Viktor Hovland and Corey Conners. He did it on a day when only eight other players managed to break par. He was two shots better than anyone else in the field on a golf course that was soaked from a steady rain throughout the day.

All it added up to is that Koepka has a chance to cement his legacy as the most prolific major champion of this generation. A win here this week would be his fifth career major, breaking a tie with Rory McIlroy for most of any active player under the age of 40. It would tie him with golfing legends such as Byron Nelson and Seve Ballesteros and put him just one behind Phil Mickelson and Lee Trevino. He would join the game's two biggest names, Tiger Woods and Jack Nicklaus, as the only players to win three PGA Championships since the event moved to stroke play in 1958.

Koepka found himself in a similar position just a month ago when he took a two-shot lead into the final 18 holes at the Masters. Then the man who had a reputation as a cerebral assassin in major championships did something uncharacteristic: he began to play not to lose. Koepka let the lead slip away as Jon Rahm roared past him for the Green Jacket.

Koepka vows never to let that happen to him again. "To just never think the way I thought going into the final round," he said following his round on Saturday. "Learning what I learned at Augusta kind of helped today…I won't do it again the rest of my career. But that doesn't mean that you can't go play bad. You can play good, you'll play bad but I'll never have that mindset or that won't ever be the reason."

The opportunity of adding another Wanamaker Trophy to his collection is now starring Koepka right in the face. He did it with a late flurry of birdies to finish his third round, including a 46-foot putt on the 17th hole that left the New York gallery recognizing that they were witnessing greatness. After publicly questioning to Netflix cameras whether he would ever be able to compete against the game's best just one year ago, Koepka will take the 54-hole lead for the second straight major championship, the first player to do that since McIlroy in 2011.

Can anyone challenge Brooks Koepka on Sunday?

Conners and Hovland are his closest chasers, but they don't have the pedigree that Koepka does. Conners has never been in this situation before. Hovland has, and his experience hasn't been pretty. He had the lead heading into Sunday last July at St. Andrews but fell to fourth after a closing 74, then was in contention again at the Masters but shot another 74 and never seriously challenged the leaders. Then there is Koepka's old nemesis and LIV Golf colleague Bryson DeChambeau, who was paired with Koepka on Saturday in a grouping that didn't feature much small talk between them and enters the final round three shots off the lead.

Koepka's first four majors came in a rapid string of dominance over three years that left him as golf's biggest clutch performer. His last came in 2019, a four-year drought that has seen that reputation shaken by blown Sunday leads and a complete loss of confidence.

Which Koepka will show up to Oak Hill tomorrow? The domineering one from 2017-19 or the one who openly questioned his future in the game in front of the entire golf world? Another notch in his legacy is at stake, and a third PGA Championship will elevate Koepka into a new pantheon of the game's greats. All he has to do is survive another 18 holes.