PITTSFORD, N.Y. (AP) — Brooks Koepka says he thrives in majors because they’re the toughest tests. The PGA Championship was every bit of that on a rainy Saturday at Oak Hill, and so was Koepka.

Koepka was at his best even during occasional downpours, and he surged into the 54-hole lead for the second straight major. He had a 4-under 66 — the low round at Oak Hill for the second straight day — and led by one shot over Viktor Hovland and Corey Conners.

Now he has to finish it off. Koepka failed to do that last month at the Masters when he had a two-shot lead, played it safe and shot 75 and Jon Rahm tracked him down to win by four.

“I know what I did,” Koepka said. “I promise I won’t show up like that tomorrow.”

The last player to have the low score in the second and third rounds of a major championship was Tiger Woods in the 1997 Masters, which he won by a record 12 shots.

Koepka, who was at 6-under 204, won’t have it that easy.

Conners played Oak Hill like a U.S. Open — that’s what this PGA Championship feels like — by opening with two birdies and 13 pars that kept him in front for so much of the wet, grueling day. And then one swing changed everything.

He was in a bunker right of the 16th fairway when he hit the ball so thin that it disappeared into the lip of the soggy turf. It was plugged deep in the sod, and Conners had to drop it in gnarly rough on top of a mound framing the bunker. He did well to advance that toward the green into more thick grass and took double bogey.

Conners, in control for so long, had to settle for a 70.

Hovland overcame mistakes early with three birdies in a five-hole stretch around the turn. But then the Norwegian failed to take advantage of the scoring stretch — Nos. 13, 14 and 15 — and took bogey from the bunker on the 18th hole for a 70.

He will be in the final group of a major for the second time. Hovland was tied with Rory McIlroy at St. Andrews last summer and closed with a 74.

Missing from all this activity was Scottie Scheffler, the No. 2 player in the world, who started with two straight bogeys and didn’t make a birdie — his only one of the round — until the 14th hole. He shot a 73, but is still very much in the mix.

So is Bryson DeChambeau, who played with Koepka and took double bogey on the sixth hole for the second straight day. He ground out a 70 and was three shots behind.

McIlroy was about like the weather — promising and then bleak — during a wild round that ended with a par save for a 69. He was among only seven players under still under par, but still five shots behind the four-time major champion Koepka.

Asked if there was a 65 at Oak Hill, McIlroy said he would have to keep mistakes off his card.

“I have to believe that there is a score like that out there because … I’m going to have to shoot something like that to have a chance to win,” he said.

And he will need some help from Koepka, who has a 54-hole lead in his second straight major.

Oak Hill in pleasant weather has been a brute. Rain came down at the start of play and never really let up except for a brief burst of sunshine and shadows, and then the showers returned. Fairways were framed by umbrellas. The rough was thick and wet. McIlroy was among players who wore their caps backward to keep rain from dripping off the bill.

Koepka motored along, and he was particularly sharp with the putter on the back nine. He holed a 15-foot birdie putt on the 12th and made one from 18 feet on the par-5 13th. The real boost came on the 17th, when he rolled one in from just outside 45 feet.

“Felt like it was a bit more aggressive today,” Koepka said of his putting. “Especially on the back nine, and putts started banging in the back of the hole.”

And then came Conners’ blunder on the 16th, Hovland’s bogey on the 18th, and Koepka was all by himself atop the leaderboard as he chases a fifth major, and a third PGA Championship. Also at stake: A victory moves him to No. 2 in the Ryder Cup standings. Because Koepka plays for LIV Golf, he can only earn Ryder Cup points in the majors.

Justin Rose joined Scheffler at 2-under 208, still very much in range. And no one appears to be having more fun than California club pro Michael Block. He had another round of 70 and tied for eighth, the first club pro to be in the top 10 after 54 holes since 1990 at Shoal Creek.

Even Koepka’s great run along the back nine didn’t look like it would be enough to catch Conners, and then that changed on the 16th hole. Conners swung and then tried to figure out where it went, looking up in the air, until realizing it shot right into the lip.

“Wish I could have that one back,” he said.

Scheffler would like to have back his opening seven holes — four bogeys, and it could have been worse. Is shot out of wet rough on the seventh landed in Allen’s Creek and hopped out to the other side. He was bogey-free over the final 11 holes.

“I didn’t shoot myself out of it on a day where the conditions were tough and I didn’t have my best stuff,” Scheffler said. “I hung in there pretty good and didn’t post the number I wanted to, but I’m still only four back going into tomorrow. And if I go out and have a great round, I think I’ll have a decent chance.”

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