Washington - World number one Brooks Koepka birdied the 18th hole Friday, capping a three-under-par 67 to take a one-shot lead over Justin Thomas and Rory McIlroy in the US PGA Tour Championship.

Koepka posted his second straight 67 at East Lake in Atlanta, Georgia.

Under the "staggered start" format by which players were spotted strokes based on their position in the playoff standings, that put him on 13-under par -- one stroke in front of American Thomas and Northern Ireland star McIlroy.

McIlroy capped his 67 with back-to-back birdies, including a bravura finish at 18 where he was in the trees off the tee.

He used a five-wood to fire out and ended up with a good lie in the rough between two bunkers near the green.

"I felt comfortable doing it," Mcilroy said. "I made a four off a bad tee shot, so I'm not complaining."

Thomas -- who went into the tournament as the top seed, awarded a two-stroke edge after his win in the BMW Championship -- was alone atop the leaderboard at 13- under through 16 holes but slipped back with a bogey at 17 and finished with a two-under 68.

Koepka who started the week three shots off the lead, couldn't get his eight-foot eagle putt to drop at the last, but he tapped in for his fourth birdie of the day.

"I mean, the lead's always nice, so I'll take that," Koepka said. "I played good today. I putted really good. Short game was pretty solid."

Koepka had three straight birdies at the sixth, seventh and eighth, but like most he struggled on a tough back nine after a weather delay.

"The rain delay kind of killed any momentum I had," he said. "I didn't feel like I had any good golf shots after the rain delay, but that's part of golf. Everybody's got to deal with the same thing. I just didn't execute."

Thomas also had three front-nine birdies, but he was one-over on the back. He, too, said he "kind of had a hard time getting back into it" after the delay.

"But if I continue to drive it like I did today, I feel like I can really do some damage this weekend," Thomas said. "I just have to realize that I played really well today."

American Xander Schauffele was alone in fourth, his eagle at 18 giving him a 69 that put him two shots off the lead.

Thomas said the day "felt more normal" after the oddity of arriving at the first tee of the tournament on Thursday already credited with a two-shot lead.

The new format is designed to ensure that whoever wins the season finale will also claim the cumulative FedEx Cup playoff title and its $15 million top prize.

Leading second-round scores on Friday in the US PGA Tour Championship at East Lake in Atlanta, Georgia (USA unless noted, par 70. Totals to par reflect "staggered start" format):

13-under

Brooks Koepka 67-67

12-under

Justin Thomas 70-68

Rory McIlroy 66-67

11-under

Xander Schauffele 64-69

9-under

Paul Casey (ENG) 66-67

7-under

Patrick Cantlay 70-71

6-under

Chez Reavie 71-64

Patrick Reed 70-70

Matt Kuchar 66-72

5-under

Adam Scott (AUS) 68-70

4-under

Tony Finau 70-69

Jon Rahm (ESP) 68-72

Abraham Ancer (MEX) 72-69

3-under

Im Sung-jae (KOR) 67-71

2-under

Jason Kokrak 71-67

Tommy Fleetwood (ENG) 69-70

Corey Conners (CAN) 68-71

Gary Woodland 68-73

Hideki Matsuyama (JPN) 66-75