Johnny Miller in 1973 shot an 8-under 63.
Justin Thomas has set a US Open record in becoming the 31st golfer to shoot 63 in a major championship.
His ball ended up just over six-feet away, and Thomas looked likely to gain the outright lead with an eagle.
His round began with back-to-back birdies, and although he dropped a shot on the fourth, he responded with an incredibly inventive birdie putt on the 5th that kick-started momentum for his record-breaking low round.
When he eagled the par-5 18th, he became just the fifth player ever to finish with a score of 63 in U.S. Open history, making him the first player since Vijay Singh accomplished the feat at Olympia Fields in 2003.
Srikanth beats World No:1 to reach Indonesia Open final
Srikanth fought like a man possessed to outclass Korean Ho in an energy-sapping men's singles match that lasted 72 minutes. With this win, Srikanth improved his head-to-head record to 3-4 against Son; he had lost his last four matches against Son.
Thomas emphatically sunk six birdies over the front nine then responded with an eagle, three birdies and a bogey on the back. "I had no idea about the relation to par, so that was definitely a big bonus".
Thomas, who shot a 59 and has three victories this season on the PGA Tour, also moved into the lead with his putt at 18.
Faced with 299 yards to the hole, Thomas hit a majestic 3-wood that landed just short of the hole before rolling eight feet past.
The leaderboard at the U.S. Open is looking about as crowded as an L.A. freeway at rush hour. He is at 11 under, two shots ahead of Charley Hoffman and Tommy Fleetwood.
"I feel comfortable when I get in contention", said Thomas.