Benign conditions on Thursday made for a feast of low-scoring, with a record 44 players dipping under par - the most ever in the first round of the US Open. Friday's round included five birdies and two bogeys.
He picked up one shot on his first nine after an opening-round 79 but a double bogey on the fifth and a second-round 75 have him 10-over for the tournament.
"Usually when you shoot even in the U.S. Open and you're one off the lead, you're not six down afterwards".
The 30-year-old from Georgia had never gone past the second round in a US Open before this year, missing the cut on his two previous visits in 2012 and 2015.
Despite having a huge power advantage over most of the field, and displaying excellent form with his irons, Koepka was unable to capitalise on a few good birdie chances. I mean, if I can make four birdies around here, you know, that'd be pretty good. More important, he was happy with how he played Friday and remained optimistic that he could carry that over to the weekend. I couldn't possibly shoot any higher than I did, I just struggled on the greens.
Rickie Fowler, on the verge of being left behind, rallied with three straight birdies and shot 68.
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Thomas, 24, lit up Erin Hills during his third round as nine birdies and an eagle helped him break the record for the lowest score to par in the tournament's history. Holmes join Fowler a shot back and five other players are within two shots of the lead.
Friday wasn't almost as favorable for the world's three-top ranked players, none of whom will move onto the weekend.
And despite carding four birdies in his last six holes for a 71 on Friday, the four-time major victor saw his own pre-event prediction come true, having said on Tuesday that anyone who could not hit the wide fairways "might as well pack your bags and go home".
"It was definitely a lot more like a US Open today than yesterday the greens were a little quicker again", Leishman said. It's been unbelievable. The amount of support that I've received every hole I walk up to, every tee box, it's been unreal.
This assortment at the top was made possible when the wheels came off Fowler's game after his lights-out, record-setting 65 at Erin Hills golf course on Thursday. Masters champion Sergio Garcia returned a tidy one-under 71 to leave the Spaniard four back and in contention for a second straight major. I've pictured winning the U.S. Open a lot of times before.
For players like Jordan Spieth (73) and Johnson, it was a matter of not making enough putts.
But while Casey was relieved after his gutsy fightback, it was back t the drawing board for McIlroy and Day after their disappointing exits.
"I was in the hay too much over the last couple of days", Day said.