He struggled with his chipping, then three-putted for a seven.
"I felt bad about it", said Koepka, who would bogey the hole.
Jordan Spieth says he doesn't feel any extra expectations at the PGA or any major, but he admits to feeling the pressure.
What he does have is a positive attitude and confidence from having recently won the third leg of the career grand slam. It was just the bunker play and the greens.
Rory McIlroy, a two-time victor at Quail Hollow, and defending champion Jimmy Walker are among those who start in the afternoon half of the draw.
Spieth said after the first round.
Spieth played in the 2017 glamour threesome which included the winners of the Masters, the U.S. Open and the British Open. He was happy with his round because it was hard to make putts.
With Quail Hollow recently installing a new breed of Bermuda grass on all 18 greens, Day was satisfied with his round on lightning-quick putting surfaces.
Starting from the 10th, Spieth made the turn in level par after a birdie-bogey opening nine, but he stumbled badly on the back, bogeying the first, fifth and sixth holes to find himself three over.
"I've gone through a little bit of a plateau here, and hopefully I can change that this week, especially with the past experiences that I've had competing in the PGA Championship". Charley Hoffman had the lone birdie on the 18th, and the only two birdies on the 17th belonged to Ernie Els and Tommy Fleetwood.
Video posted on the PGA of America's Twitter feed showed Koepka checking on the marshal and signing a glove for him as he laid on the ground.
Fortunately, the man appeared to be Okay. That means fans watching at work got to see Koepka hit a drive into the crowd on the 16th hole which made contact with a marshal's head and left him bloodied.
Eleven years after winning $US1 million off Donald Trump, unheralded Brisbane pro Stuart Deane is hoping to take the cash from the world's best golfers at the US PGA Championship.