His 9-under 63 was one stroke better than Johnny Miller's round of 63, which was 8-under at Oakmont in 1973.
Both players are living in the penthouse on the leaderboard.
Count former Taylor County and University of Kentucky star J.B. Holmes among those in the mix.
Fowler had six birdies against two bogeys on Saturday and enters the final round in fifth place and in prime position to attack the course.
There is a palpable excitement around the grounds at Erin Hills due to the packed leaderboard that portends a thrilling weekend and the fact that the course has shown well-challenging yet fair.
"I'm optimistic with where my game is", he said. "It's got your attention on every hole, because you know if you miss the fairway, you're going to pay the price".
"I felt the most calm I have in a major in a long time this week", said Day, who arrived last Friday.
"I'm going to enjoy my time tonight with my little girl and my wife".
Three more birdies on his inward nine took him to seven under and a piece of US Open history. No matter what that's something when you're always going to walk up the 18th green with your best mate. You've also got the young Englishman Fleetwood and the long-driving Koepka sitting near the top of the table, ready to pounce. Some of it nearly takes the bombers out of it.
Then there was the Par-5 18th hole. McIlroy could only take some optimism away from his finish. "I have a tee time on Saturday (and) so you just kind of learn along the way to never really give up".
The only good thing about his opening round of 77 was that it was the lowest of his group, with Tiger Woods shooting 80 and Rickie Fowler an 81 for a combined total of 28 over par. "Still 7 (under par)". "It will be a pleasure to go out on a Sunday trying to win a major".
That's what happened as Stricker made it exactly on the cut line.
Then, inexplicably, he lost his putting touch.
One shot back. Jamie Lovemark. "I'm looking forward to my shot at it". "I couldn't possibly shoot any higher than I did". PGA Tour rookie Xander Schauffele didn't make a bogey at Erin Hills until his 27th hole, had his hiccup with a double bogey on the par-3 13th hole but still managed a 73.
McIlroy was never in the short grass from the 11th hole to the end on Thursday when he opened with a career-worst 78, and he didn't do almost enough in the second round until it was far too late.
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