Miller, who posted his 63 in the final round of the '73 Open on a par-71 course, was unimpressed that Thomas achieved his (a U.S. Open scoring record relative to par) on a par-72 track that offered players wide fairways and soft conditions.
As Brian Harman began to fade, Koepka poured it on with birdies over the next three holes, lightly pumping his fist after each one.
Eventually though it was not enough, although a round which contained eight birdies suggested he may not have long to wait to win his first major. However, the 26-year-old then bogeyed the sixth after hitting a poor chip across the green and dropped another shot on the eighth after firing his approach over the green.
"Yeah, I like it", he said about Erin Hills.
England's Tommy Fleetwood followed two shots back, one ahead of Rickie Fowler and Charley Hoffman.
The much-maligned site of this year's national championship has been giving up birdies and low scores, very unlike a U.S. Open Course.
Justin Thomas had high hopes entering Sunday's final round of the U.S. Open that he could be the one lifting the trophy against the setting sun encompassing Erin Hills.
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Around 70 people are missing, according to Britain's Press Association, and identification of the victims is proving very hard . The tragedy has provoked a enormous response from nearby communities that have donated food and shelter to the victims.
Koepka's win extended a remarkable run of victories by players who had never previously won a major. Only six players had ever reached double digits under par in the previous 116 times at the U.S. Open. Of all his birdies, that 8-foot par putt might have been as big as any.
And he succeeded as US Open champion his good friend Dustin Johnson, who missed the cut at Erin Hills but gave him a pep talk on the phone after Saturday's third round.
But having held the 54-hole lead, and playing the best golf of his professional career, Harman struggled to find much satisfaction in almost coming in first. When he pushed a 30-foot birdie try on No. 12 a full 12 feet past the hole, he set himself up for bogey.
Australia's Marc Leishman shot a final round 75 to finish at one-under, in a tie for 27th.
Despite winds gusting up to 25mph which forced tournament officials to change the pin position on the par-three 13th, Spieth showed what was still possible with a closing 69. Fowler started one shot out of the lead at the Masters this year and shot 76.
Brian Harman had the lead at 12 under coming into the day.
He hit a good putt on No. 2 that got caught the left edge of the cup and spun out, and settled for bogey. While stronger winds made tee-to-green play more hard during the final round, they may have also helped Spieth on the greens where he needed only 29 putts. Spieth made birdies on the first two holes, both of which are playing downwind.