Brooks Koepka hits his tee shot on the 18th hole during the third round of the 100th PGA Championship at Bellerive Country Club in St. Louis. (SHAWN THEW/EPA-EFE/REX/Shutterstock)

It was such a long day at the PGA Championship that some of them had grown stubble by the end of it. With so much action happening all across Bellerive Country Club over so many hours, the challenge was to hold up under the withering pace in the heat — and that was its own kind of enervating pressure for leader Brooks Koepka, what with the legions chasing him, including Tiger Woods. But Koepka proved as hard as the course was soft.

You could pardon Woods for looking like he needed a shave and a fresh shirt after almost 12 hours of golf, with a 7 a.m. start to complete his rain-halted second round followed by the third. He had a raffish five o’clock shadow after playing 29 holes and carding a pair of 66s that put him just four strokes back at 8 under par, and that represented the finest charge he has mounted in a major championship in several years.

“It’s not necessarily physical,” Woods said. “It’s mentally grinding that hard for 29 holes in this heat. . . . I’m done. I’m done with the golf side of it today. I’ve had enough.”

Woods was among 10 players within four shots of Koepka, the two-time defending U.S. Open champion who is seeking his third major title in his past six outings. Superficially, the rock-chinned, burly-chested Koepka looks like an exercise in pure bashing power golf, of muscle meeting technology. But he demands consideration as a better, more complete and more delicate player than that. Koepka is seeking to become only the fifth player to win the U.S. Open and the PGA Championship in the same year, and the list he would join is formidably elite: Gene Sarazen in 1922, Ben Hogan in 1948, Jack Nicklaus in 1980 and Woods in 2000.

Those happen to be the most complete players in the history of golf. Koepka just may be that kind of complete, too.

“I feel like if I do what I’m supposed to do, I should win the golf tournament,” he said.

The challenge for the field will be to catch a player so physically and mentally tough that he lifts weights even during major championships. Koepka is not just strong and long, though; he’s straight off the tee and a sound putter, and he showed off an array of touchy shots at Bellerive’s greens, taking full advantage of a golf course that was so yielding that it felt bed soft and spongy underfoot.

“They’re so nice to hit some wedges off of,” he said. “You can really control the spin, the flight.”

He parachuted shots that dropped straight on top of the pins for a 66 that included a stunning 30 on the front nine and put him at 12 under par.

There were so many other big names jostling for position that at one point it felt more like a car race than a golf tournament. Just two strokes back was Adam Scott, who had the low round among the leaders with his 65. Among the other chargers and faders were Rickie Fowler, in a three-way tie for third at 9 under, the eighth time in his career that he is in the top five entering the final round of a major. Then there was defending champion Justin Thomas in the crowd of six another stroke back, a group that included Jason Day, Stewart Cink and Charl Schwartzel.

As Woods said, “Guys are making birdies from everywhere.” No one made more in one stretch than Woods, who electrified the gallery with a 31 on the front to start his third round. He rained his short irons on the downy greens for five birdies and was two strokes off the lead as he made the turn, setting off a chain reaction of noise across Bellerive. The crowds crooned to him, imploring him to keep it going. But it came to a dead halt on the back nine as he settled for nothing but pars.

Still, it was the biggest move he has made in a major since the 2011 Masters, when he came from eight shots back to briefly lead before finishing fourth.

“It’s plugging; we’re able to hold 4-irons, 5-irons, whatever we want, at the flags,” he said.

The question is whether Woods will be able to keep up such a hot scoring pace for another round and fight through such a sluggers’ row of fellow established champions.

“This golf course is stacked right now, and everyone is bunched,” he said.

Still, there was enough trouble if you got too aggressive or sloppy, or decided you didn’t quite belong in that company.

“It can show its teeth if you’re not driving it well,” Thomas said.

Indeed, Jordan Spieth had been fighting a bad swing all week and finally paid the price for it. He drove his ball in the trees at the par-4 12th hole, then tried a risky recovery shot through a narrow gap that ricocheted, taking triple bogey that flatly knocked him out of contention.

“Just very frustrated that I’ve worked my way into a chance to win this tournament, just to kind of throw it away on a bad decision,” he said.

He had been on the verge of a low number that would have vaulted him into the thick of it.

“I know I can shoot around a 7 or 8 under around here. I know that that’s in the bag,” Spieth said.

Gary Woodland has been at the top of the leader board for three days with the swagger of a dancing bear, but he finally found the altitude too much and took a mortifying 7 at the par-4 10th. Woodland’s approach spun back into a bunker, and he failed to get it up and out of the sand. He was so rattled that he then chopped his second attempt all the way across the green and into another bunker on the opposite side. Worse, the ball landed in a divot of unraked sand. He barely managed to scrape that one out — but it stayed in the rough of the upslope.

Despite the triple bogey, his round of 71 left him in a tie for third.

He was the rare outlier, a relatively unproven player among the logjam of established champions who will be chasing Koepka on Sunday.

“Yeah, there’s a lot of star power,” Koepka said. “And it should be: It’s a major championship.”