ERIN, Wis. — Justin Thomas stepped up to his putt at the fifth hole Saturday at the U.S. Open and hit the ball backward. All part of the plan.

Oh, I see. The birdie was the third of the day through five holes for Thomas, and he followed it with another long birdie at No. 7. Then came two more at 8 and 9, and three followed on the back nine. Then, at the par-5 18th, he hit a fairway wood to within eight feet of the hole. Aiming straight for the cup, he sank the putt for eagle and entered the record book.

With his 9-under 63, he broke Johnny Miller’s 1973 record for the lowest round to par at a U.S. Open. Thomas left the course atop a crowded leader board by two full shots, gaining precious separation at an event where there was little before.

Thomas, 24, is probably best known as the seventh player in PGA Tour history to shoot a 59, doing so in January at the Sony Open, but now that very low round likely will be seen as merely his second-best 18-hole outing of the year. He’s in the hunt for his first major win, having never finished better than tied for 18th at a major.

Besides becoming the lowest round to par in U.S. Open history, edging Miller’s legendary 8-under 63 at Oakmont near Pittsburgh, Thomas’s round rang up some other distinctions: first 63 in a third round, fifth 63 in a U.S. Open, 31st 63 in the history of major tournaments, which have never seen a 62.

The unprecedented round actually included two bogeys (on Nos. 4 and 10). “Bogeys happen,” Thomas said, “and if you let it go with your or let it stay with you, then it’s even worse than the bogey.”

Three shots sparkled in particular.

On No. 18, Thomas stood 299 yards from the pin and sought his magical 3-wood to send it within six feet. “I obviously needed to nuke it,” he said, “but I just felt like I could get it up in the air enough to hold the green as soft as they were. And it came out nicely.” On the green awaiting the eagle putt, his hands trembled, but only because, he said, he hadn’t packed sufficient food and felt hungry. He made the eagle anyway.

On No. 5, he bristled at where the ball came to rest on the edge of the green, then produced a geometric wonder that headed out sideways, turned right and looped around to the cup for a birdie. “I was trying to get over the fact of how mad I was that I didn’t have an eight-footer for birdie like I felt I should have,” he said, “but it just was one of those that you try to find the high point. Just find the fall line.”

And, like a U.S. Open veteran even at a U.S. Open that doesn’t feel like a U.S. Open for all the red, Thomas cited a par.

He had birdied Nos. 1 and 2, but extolled a 6-iron he hit into No. 3, from 204 yards away, with the ball above his feet, with the left wind. “And I just pured the 6-iron right at it,” he said. “You know, that’s something to where a lot of people would just be like that’s another shot I made par. But I don’t know. Something about that shot kind of calmed me, and it made me very comfortable for the day.”

It confirmed that the Louisville native has a penchant for unusual hotness. It followed by five months upon his 59 at the Sony Classic in Hawaii, which became the seventh 59 in PGA Tour history and also closed with an eagle. It gave Thomas a plausible chance at a fourth title in a season already rich with three (and with four other top-10 showings). It forced the reasonable question about whether, in these moments, the No. 13-ranked Thomas considers himself the best golfer in the world.

“No reason to answer that,” he said. “I can’t win with the answer to that question.”

Thomas is sponsored by Polo Golf, so you know where to look for those pink pants.

Thomas played his college golf at Alabama, and one Twitter user challenged his choice of what seemed to be a very Auburn-esque orange shirt for Sunday. But Thomas was quick to say that he’d never go there.

Bonesteel contributed from Washington.