The perfect pairing? PGA Championship’s final group of Phil Mickelson, Brooks Koepka might be.

Brooks Koepka was 2 years old when Phil Mickelson turned pro.

KIAWAH ISLAND, S.C. — Phil Mickelson was annoyed.

It had nothing to do with his golf. That was going splendidly Saturday with birdies on two of his first three holes to open up a three-shot lead that would peak at five before stumbling during the third round of the PGA Championship.

But as Phil addressed his second shot on No. 4, he was looking straight into a drone.

“Could the TV guys get the drone out of the line of my shot,” he said to anyone who would listen on the course.

“It’s annoying.”

That drone, as it turned out, was the least of Mickelson’s problems by the end of the day. A larger one started looming on the back nine, one that four years ago turned majors into his personal playground, having won four, and once again has been under the radar this week as he continues to recover from knee surgery.

PGA Championship: Leaderboard | Photos | How to watch | Tee times

Now, Brooks Koepka is Mickelson’s biggest annoyance.

“Feels normal,” said an emotionless Koepka minutes after posting a 2-under 70 to get to 6-under for the tournament, one shot behind Mickelson.

“I’ve got a chance to win, so that’s all I wanted to do today is not give back any shots and be there tomorrow with a chance,” Koepka said. “And I’ve got that.”

Koepka was 2 years old when Mickelson turned pro. Mickelson’s first major championship, the 2004 Masters, came eight days after Koepka’s 14th birthday. Sunday, the two will be paired with Koepka seeking his fifth major, third PGA Championship, and Mickelson seeking his sixth major and second Wanamaker Trophy.

“I’m playing really well and I have an opportunity to contend for a major championship on Sunday,” is how Phil, 50, summed up the day.

Koepka, 31, made up five shots in six holes to catch Mickelson, who appeared as if he was going to head into Sunday’s final round with a comfortable lead and a heavy favorite to become the oldest ever to win a major. But after playing his first 10 holes in 5-under and leading by five shots, Mickelson went bogey, double on Nos. 12 and 13. Koepka caught him with birdies on 12 and 16, but gave one back with a bogey on 18.

[vertical-gallery id=778104757]

That set up the pairing between two titans, one beyond his prime but finding the Fountain of Youth and the other an indomitable foe when it comes to majors, wounded knee or not.

Koepka, ranked 13th in the world, admitted he is not close to 100 percent after undergoing surgery two months ago to reattach a ligament in his right knee. He still cannot fully squat to read putts and looks awkward when sticking his tee in the ground or retrieving his ball from the cup.

The knee has held up. But that’s only part of the reason Koepka is contending in another major. He is dialed in with a focus he saves for this stage.

Koepka is so focused on what he is doing that when asked about being in the final pairing with the Hall of Famer, he said, “Am I in the final group? I don’t know.” Luis Oosthuizen relinquished that honor by shooting a 72 and finishing one shot behind Koepka.

“It’ll be nice,” Koepka said. “At least I can see what Phil is doing.”

Koepka had an idea what Mickelson was doing early when, playing one hole ahead, he heard the roars. Mickelson played as well as he has in a very long time – his last PGA Tour win came two years ago and we’re eight years removed from his last major championship – with four birdies in his first seven holes and then going to 5-under with another on No. 10.

Koepka, though, was always lurking despite what he believes was “the worst putting performance I think I ever had in my career.” As a result, Koepka hit the putting green for more than 30 minutes following his round. He called it a “speed issue and “not trusting” his stroke.

“It was just maybe felt a little slow,” he said about the greens. “I’ll go figure this out here shortly.”

The swing hole that opened the door for Koepka was No. 13. Both Mickelson and Oosthuizen, his playing partner Saturday, put their tee shots into the creek that runs along the right side of the hole. Oosthuizen managed to bogey the par-4 hole. Phil had to re-tee and missed a 13-foot putt for bogey.

[listicle id=778104922]

The double was his first of the tournament. In a span of three holes, Mickelson’s lead went from five to a single shot.

While Koepka was working on the putting green as the sun was setting on Kiawah Island, Mickelson was on the range. The driver was good to “Lefty” the first two rounds so much so he was 10th in the field in Stokes Gained: Off the Tee on Friday.

On Saturday, he was 70th.

He blamed his focus, something he has struggled with as his world ranking has plummeted to 113.

“I felt I had a very clear picture on every shot, and I’ve been swinging the club well, and so I was executing,” Phil said about the first 10 holes.

“Even though it slipped a little bit today and I didn’t stay as focused and as sharp on a few swings, it’s significantly better than it’s been for a long time. So I’m making a lot of progress, and I’ll continue to work on that and hopefully I’ll be able to eliminate a couple of those loose swings tomorrow.”

And if he doesn’t, Mickelson will have some company in the five-majors club.

[mm-video type=playlist id=01es6rjnsp3c84zkm6 player_id=none image=https://golfweek.usatoday.com/wp-content/plugins/mm-video/images/playlist-icon.png]