The American, 29, won two majors this year after retaining the US Open and taking the PGA Championship too.
You would think, then, that he would be perfect adept in rolling in a putt from two foot.
But no. Koepka needed to whole his putt to win the 15th hole against Sergio Garcia and Rory McIlroy – but what happened next was a disaster.
He somehow contrived to clip the left lip as the ball circled round the cup and stayed out.
Ryder Cup fans gasped in disbelief at what they had seen at Le Golf National while others took to Twitter to discuss what they had seen.
“That Koepka lipout just perfectly discribes this American Performance,” wrote one.
“Koepka missed from 2 feet. Solid focus there by the power lifter. #rydercup,” said another.
“Hahahahahahahaha Koepka misses a one footer!!!!!! Good god this US team is pathetic. #RyderCup,” taunted one European fan.
RYDER CUP LIVE: UPDATES FROM DAY TWO AT LE GOLF NATIONAL
While another said; “LOL, Koepka just missed one from 20 inches. I’d ask “why were they making him putt that?” but I guess I found out. Finau rolled in a 2-footer for par to give the U.S. the win.”
“How does Koepka miss a 2 footer? I mean seriously insane” pondered a fellow viewer.
Team Europe captain Thomas Bjorn had earlier warned his Ryder Cup players not to give putts away at Le Golf National.
Bjorn linked up with former English pro Nick Dougherty for a Sky Sports feature ahead of the Ryder Cup.
The pair took on one another in a three-hole round with Bjorn taking the first.
Dougherty holed a 12-footer for it to go into a decider and the light-hearted match went down to the final putts.
Bjorn gave Dougherty an eight-footer to ensure he got par, to which the Englishman joked: “That’s the spirit of the Ryder Cup!”
But Bjorn stopped him in his tracks and said: “No, it’s the spirit of golf.”
Dougherty then joked there wouldn’t be too many of those given away in Paris, to which the European captain replied: “I hope not. They’ll be in big trouble if they give too many of those away.”