Scott is tied in 2nd place at 5 under with Jordan Spieth after a best of the day round of 64 saw him jump 39 places on day two, a frustrating three-putt bogey at the 17th his only blemish in what was an otherwise sublime round of golf.
Following his opening round of 71 yesterday Scott needed to make progress today and with four birdies in his first five holes he was headed in the right direction.
Further birdies at the 11th, 13th and 14th holes had him on track to equal or even better Koepka's opening 63 and, perhaps with two more birdies, create a new major championship scoring record of 61.
That hope remained alive with two holes to play and his tee shot at the 17th left the door open for one of those birdies. He ran his 25-foot putt three feet past however and then missed the return for his first bogey of the day.
Scott would then save par at the last after missing the fairway and the green to finish with 64 and although seven shots back he is well poised should Koepka falter at all over the closing stages.
With the long putter back in the bag his putting both yesterday and especially today has been good. It has been his 5th putter this season despite a reasonable putting year overall but he seems to have found a comfort zone with this one.
Looking back Scott had mixed emotions of his finish although most were positive.
"I thought, whether it was low or possible leaving the 15th green, you know, 16, 17, 18 today are actually very gettable with the tee up on 17," said Scott when considering the possibility of 62 or better.
"I mean, it was a fleeting thought. Not happening at the end of the day, and in the end I was very happy to get it up-and-down for 64 on the last. Look, overall, you shoot 64 in a major, you've had a great day and I did today. It was a great start, and managed to keep it going for a lot of the day.
Scott knows he has a big task to chase down Koepka but he was keen to keep up the positive talk and keep things in perspective.
"I think there's doubles left and right out there once you get out of position. Hey, if the guy (Koepka) 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.
"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, I know he's won three majors and I know he seems impenetrable at the moment in this position, but at some point he's got to think about it."
Well-deserved ovation for Adam Scott.May 17, 2019
Jason Day led the Australians after day one but three bogeys in his first four holes today had him on the back foot and, in the end, he was forced to either par or birdie the last to make sure he was around for the weekend. He played it beautifully, holing a ten footer for birdie to finish a shot inside the cut-line.
Also on that score was Cameron Smith whose round of 70 kept him alive for the weekend while Lucas Herbert, playing in his very first PGA Championship holed a 30 footer at the last for birdie to force his way into the weekend field on the number.
Koepka added a round of 65 to his opening 63 to establish a record score for the opening 36 holes of a major and while it appeared flawless he felt there were areas for improvement ahead of the weekend.
"This probably sounds bad, but today was a battle," said Koepka. "I didn't strike it that good. I was leaking a few to the right. But I don't think -- the way I hung in there today and battled it, I think that was probably more impressive than yesterday, not having your A game but still being able to shoot a great score. I was very, very pleased with the way I played today."
A return to former putting coach Jeff Pierce appears to have played a key role in an excellent display on the greens of Bethpage Black thus far.
"We didn't work together for about eight months, nine months, I guess, is probably a good guess," he explained referring to time away from Pierce. "And then I just got so lost and so uncomfortable, I felt like I needed to get back to where I was.
"I started getting too mechanical, and if you know me, that's not me, to start thinking about the stroke or thinking about where my hands need to be or where shoulder position is or anything."
Spieth and Scott are seven from the lead but another shot back are Dustin Johnson, Daniel Berger, Matt Wallace, Kelly Kraft and Luke List.
Johnson's round of 67 has him well enough poised should Koepka make any mistakes. He is after all the world number one and with 15 top tens and a win in major championship golf and just as he did at the Masters a weekend charge is not beyond him.
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