Adam Scott plays his shot from the 18th tee during the second round of the PGA Championship. Photo: Peter Casey/USA TODAY Sports

BETHPAGE Australia's Adam Scott isn't going to roll over and let runaway 36-hole leader Brooks Koepka win the PGA Championship without putting up a serious fight.

The 2013 Masters winner nearly matched Koepka's day-old Bethpage Black course record 63 before settling for a six-under par 64 on Friday and a share of second with Jordan Spieth at seven shots adrift entering Saturday's third round.

Defending champion Koepka, also winner of the past two US Opens, has the largest lead in modern major golf history after two rounds, and the lowest 36-hole total in major golf history at 12-under 128.

But like everyone else, the US star is only half done.

"Yeah, I know he has won three majors. I know he seems impenetrable at the moment in this position, but at some point he's got to think about it," Scott said.

"If he didn't have a hot day tomorrow, the gap narrows and there's pressure over whatever lead he might have or might not on Sunday.

"Hey, if the guy can just keep doing that for another two days, then there's not much you can do. But I think someone, hopefully me, will chip away tomorrow and sneak up in the right direction."

Koepka seeks his fourth major win in his eight most recent major starts. It's like when Tiger Woods won his first 14 major titles from 54-hole leads.

"It has to come to an end eventually, that good front-running," Scott said. "Let's hope it's not 12 years like Tiger's front-running lasted."

Scott started his day with stunning birdie putts from 25 feet at the first hole, 38 feet at the second and 27 feet at the par-3 third then added a 14-footer at the fifth.

"I came out and they just started rolling in and didn't think much about it. I felt good with it," Scott said. "It was a great start. Managed to keep it going for a lot of the day."

Scott birdied three of the first five holes on the back nine and thoughts of super-low scores drifted into his head before reality in the form of a two-foot par miss at the par-3 17th produced his lone bogey and a 64.

"I thought, whether it was low or possible leaving the 15th green, 16, 17, 18 are actually very gettable," Scott admitted. "It was a fleeting thought. Not happening at the end of the day. I was very happy to get up-and-down for 64 on the last.

"I've just got my head into a good place this week. I feel like my game's in a really great place. If I can get out of my own head a little bit and just play and swing, I think good results are there."

Scott, whose third behind Koepka and Woods in last year's PGA was his best major finish since 2013, knows he needs something special at the weekend.

"Whether I'm six back, seven back, equal lead, to win a major, you're going to have to do some great stuff over the weekend.

"That's going to require some really great golf and when you're behind I just can't afford to make many errors. You can accept a bogey but probably not more than one a day the next couple days."

AFP