Johnny Miller shot 63 at the 1973 US Open but it was at the par-71 Oakmont, with this week's venue Erin HIlls being a par-72.
His ball ended up just over six-feet away, and Thomas looked likely to gain the outright lead with an eagle. On the par-5 18th, he sunk his eagle putt to break the record.
American Justin Thomas carded a nine-under 63 to equal the lowest score ever at a major and roar into the third-round clubhouse lead at a helter-skelter U.S. Open on Saturday. After missing the fairway at the fourth and making bogey, Thomas added birdies at Nos. Perhaps it was to wipe off the sweat, but if this was a cap tip, he's justified. That company welcomed Thomas, who now sets the standard.
Thomas, decked out in fluorescent pink trousers, was on the move quickly with a birdie-birdie start and had an even hotter finish to his front nine, carding birdies on four-of-five closing holes, including the last three to move to seven-under.
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Another achievement was forging a partnership with Volvo to test the autonomous driving capabilities of its XC90 SUV model. The news comes less than a week after Lyft announced a partnership with self-driving auto software maker nuTonomy.
"I was just trying to get to 63, just because I know that's kind of the magic number; 62 is what everybody's been chasing", Thomas told Fox Sports after his round.
Tied at eight under are Patrick Reed (finished with a 65), Charley Hoffman (through 11 holes), Brooks Koepka (5), Tommy Fleetwood (5) and Brian Harman (4).
The 24-year-old in search of his first major title has three wins this season.