Koepka - who fired a closing 3 over 74 to finish in a tie for 4th - took aim at his playing partner J.B. Holmes who endured a brutal final round meltdown, shooting a disastrous 87 to plummet from equal 3rd to a share of 67th.
Holmes, who is a notoriously slow player on the PGA Tour, received no sympathy from his compatriot and 4-time major winner Koepka during a post-tournament press conference.
"We were on pace for 13 holes but if I'm in the group, we're going to be on pace no matter what," Koepka said.
"I don't understand when it's your turn to hit, your glove's not on and then you start thinking about it. That's where the problem lies."
Holmes dropped five shots on the front nine and, inexplicably, came home with an 11 over 46.
"It's not that he takes that long, he just doesn't do anything until it's his turn. That's the frustrating part but he's not the only one that does it out here.
Holmes drew criticism earlier this year for his pace of play en route to winning the Genesis Open in Los Angeles.
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