The 3-under mark was tied for the clubhouse lead when Koepka's day was finished and the afternoon wave was setting out.
Spieth played in a threesome alongside Masters victor Sergio Garcia and Koepka, the U.S. Open champion.
A huge gallery lined the par-five 10th hole from tee to green as Jordan Spieth started his quest for the elusive grand slam at the PGA Championship on Thursday.
"Unfortunately the good work I've done on my putting this year hasn't yielded any results because I've been putting for par". "The first hole, got off to a awful [start], I missed a four-footer, and that was kind of my day, it kind of felt like". Wasn't exactly comfortable on the greens.
Grayson Murray, who grew up in North Carolina, Peter Uihlein and club pro Rich Berberian Jr. all hit the green and made par. With some of the pin locations, these greens are the fastest greens I've ever played.
"The disappointing thing was we got put on the clock when we were a hole ahead of the group behind us and that's when my round started to go..." he rued, speaking to RTÉ Sport shortly after signing his card.
As hard as the greens were, Koepka was solid with the short stick needing just 24 putts.
"But I think through the latter part of past year, I got a little bit burnt out". The shot sailed wide right and struck the marshal near the ropes. The volunteer fell to the ground with a considerable amount of blood coming from the side of his head.
"From tee to green, it's a challenging course but reasonably. once you get on the greens, it's a different beast", Day said. He was more concerned with the volunteer, who he learned after the round, was doing OK and resting at home. I feel like I'm better prepared to be in contention over the weekend and have a chance to win.
"I'll give you an example I had 72 yards from my second shot on the eighth hole, I walked up to it and I had nowhere really to land my second shot - maybe two or three yards to land it with a pitch shot".
I've gone through what will probably and hopefully be the worst loss of my career in the most public eye that golf has. You're up at night thinking, 'OK, what do I need to do to get back to that winning form?'
"I hadn't been swinging that good". Everything else that could happen is much lesser and therefore, has probably helped me since then, to focus then and only see the positive that could come out of a situation. "I'm sure he's going to have quite a big headache". I was like, well, I still feel like crap.
Even on a 7,600-yard golf course, have a 1,176-yard shot sounds pretty ridiculous.
"I was exhausted at the end of it and I didn't have enough time to reflect on what I accomplished, but also to relax and try and replace all the energy that expelled". We've been working on that forever.
Perry, 56, sat out the entire month of July 2016, and didn't finish in the top-10 in any of his final nine events that year.
The PGA Championship is the most successful tournament for Australian's of the four Majors, Jim Ferrier, David Graham, Wayne Grady, Steve Elkington and Day the most recent in 2015.
"I just stay patient", he said. "You can definitely do that pretty quick".