And he was in no mood to begin the celebrations early as he twice snubbed a kiss from girlfriend Jena Sims before teeing off for his final round.
Sims walked with Koepka to the first tee and leaned in twice for a kiss by he rejected her overtures.
Kopeka, who went into the final round with a seven-shot lead, was so in the zone that he did not appear to know what was going on.
However, Sims did not look interested as she folded her arms in awkward scenes that were shown live on TV.
Kopeka made up for it after winning the tournament as he was pictured sharing a tender moment with his girlfriend after he was handed the trophy.
Sims, who works as a model and an actress, was quizzed on their relationship during the tournament.
“I’m so not discreet,” she said.
“I’ll just wave, and he’ll tip his hat. I’ll blow him a kiss. I’m not trying to be too low-key. If I see him and he sees me, I’m like, ‘Hi!”
World No 2 Koepka earned a winner’s cheque of £1.56million after holding off a late charge from world No 1 Dustin Johnson.
His seven-shot lead was cut to only one after four bogeys from the 11th hole.
However, Johnson dropped shots on the 16th and 17th to hand the title to Koepka.
The crowd appeared to side with Johnson but Koepka insists that only inspired him to victory.
“I’m just glad we didn’t have to play any more holes. That was a stressful round of golf,” he said.
“I’m glad to have this trophy back in my hands.
“With the ‘DJ’ chants, I was aware of what was going on. He did an unbelievable job of putting pressure on me.
“When they started chanting for DJ on the 14th, it actually helped. It helped me focus. I think it was the best thing that could’ve happened.”
When asked if it surprised him, Koepka replied: “It’s New York. What do you expect when you’re half-choking it away?”