ERIN, Wis. — It’s no secret that the U.S. Open is designed to separate the men from the boys.

What we didn’t know is that this Open would separate so many men from the tournament.

Taking the sting out of not having eight of the world’s top 12 players around for the weekend, Justin Thomas shot a record-breaking 63 on Saturday.

Despite his epic day, Thomas is one shot behind Brian Harman, who shot a 67. Thomas is tied for second with Tommy Fleetwood (68) and Brooks Koepka (68).

Fifteen players are within six shots of the lead in what shapes up as a Sunday to remember at the U.S. Open — and never mind the big names who aren’t here. None of the top 18 has won a major, making it very likely this will be the seventh straight major to crown a first-time winner.

It’s also important to note that there hasn’t been a playoff in the last eight U.S. Opens. There never have been nine straight Opens without a playoff.

‘‘Obviously, an awesome day,’’ said Thomas, a Louisville native who played his college golf at Alabama. ‘‘I’m not sure when it’s going to sink in. I’m just so excited to give myself a great chance to win this golf tournament. Tomorrow’s going to be fun. I’m going to be nervous, but it’s a good nervous.’’

Thomas’ 63 is the first 9-under-par round in U.S. Open history, eclipsing Johnny Miller’s 8-under 63 in 1973.

And it is another milestone in a remarkable start to 2017 for Thomas. The boyish 24-year-old shot a first-round 59 at the Sony Open in Hawaii to become the youngest among the eight players who have broken 60 on the PGA Tour. He then backed it up with a second-round 64 and holds the tour scoring records for 36, 54 and 72 holes.

As young as he is, Thomas said he’s very comfortable with his plan to finish this week right. The experience of building on an opening-round 59 will help, he said.

‘‘It’s similar-type stuff — low round and history stuff,’’ Thomas said. ‘‘But, obviously, I enjoyed going low. When I get it going, I don’t fear, like I used to. I’m like, ‘Let’s get to 8, let’s get to 9,’ whatever it is.’’

When the cut came out on Friday, Erin Hills was shaping up as the Conspicuous by Their Absence Open. For the first time since the world rankings debuted in 1986, the top three players all had missed the cut at a major. What’s more, this course had seemed a perfect match for the considerable skills of No. 1 Dustin Johnson, No. 2 Rory McIlroy and No. 3 Jason Day.

With the superstars out of it and the scores nosediving, is that good for the U.S. Open?

‘‘As long as it’s a good tournament, it’s good for the U.S. Open,’’ Thomas said. ‘‘Whether it’s 20-under or 20-over, as long as [USGA officials] want a good tournament and an action-packed leaderboard.’’

With so many golfing stalwarts banished, Thomas stepped into the breach with a game as flashy as the pink pants he wore. Thomas finished a round that included nine birdies and two bogeys with an 18th-hole eagle. And he missed an eminently makeable eagle putt after driving the green on the par-four 15th.

It clearly was a good day for scoring at Erin Hills, which was softened by an overnight rain. There were 32 sub-par rounds, a record for U.S. Open third rounds.

‘‘If you’re not hitting it well, it’s still hard to hit it under par,’’ Thomas said. ‘‘It’s still Erin Hills. It’s still a U.S. Open. The scores are low, but we’re playing well. When it’s soft, no wind and we’re playing well, we’re going to shoot low scores.’’

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