It was, however, enough to get him into the final pairing of a major championship that remains wide open.
Brian Harman fired a 5-under-par 67 Saturday to get to 12-under 204 for the championship and holds a one-shot lead over Thomas, Tommy Fleetwood of England and Brooks Koepka. But a weather shift that is expected to hit for Sunday's final round may add a twist to a tournament that hasn't yet experienced U.S. Open-like conditions.
Thomas established an Open championship mark by shooting 9-under 63, which broke Johnny Miller's record for lowest score in relation to par.
Miller held the previous record after he shot 8-under in the final round of the 1973 U.S. Open at Oakmont Country Club. Thomas admitted that as he walked up the 18th fairway Saturday afternoon, he wasn't aware that he was on the verge of history.
But the record-setting performance has him on the verge of his first major championship if he is able to build off the momentum he established in Saturday's third round.
"I'm not sure when it's going to sink in or when I'm going to realize what I did," Thomas said. "I know one thing if it happened (on Sunday) and the result is what I want it to be, then I would probably have a little different feeling. But I'm just excited to give myself a great chance to win this golf tournament."
Thomas, however, is not alone in that pursuit.
Harman and Fleetwood began Saturday's third round as part of a four-way tie for the lead with Paul Casey and Koepka. Casey shot a 3-over 75 on Saturday to drop to eight shots back behind Harman.
Rickie Fowler, who led the tournament after shooting a 65 in Thursday's opening round, will begin Sunday in fifth place, two shots off the lead. Fowler shot a 4-under 68 on Saturday to remain in contention for his first major championship.
Harman narrowly missed a birdie putt on the par-5 18th hole. But with virtually no breathing room at the top of the leaderboard, Harman knows he has little room for error -- especially with high winds forecasted for Sunday's final round that could dramatically change how Erin Hills' demanding layout plays.
"(The wind is) going to blow and the scores could be a good deal higher tomorrow if the weather comes to what they're predicting," Harman said. "It could change in a heartbeat."
Fleetwood, who shot 68, overtook Thomas for the lead with a birdie at 15 and missed an opportunity to get to 13 under when his birdie putt on the par-3 16th hole rolled over the left lip of the cup.
After pars at 16 and 17, Fleetwood dropped into a second-place tie following a bogey on 18 when his fourth shot rolled off the back of the green. Despite dropping out of a share of the lead, Fleetwood will take the same mindset into Sunday's final round as he remains in contention of a major championship that he said would be life-changing.
"If someone shoots 9-under tomorrow in the top few (players), then I will have to shoot 10-under, I guess," Fleetwood said. "But you can't do anything about that stuff. I've just got to keep going."
Thomas, who said he didn't expect anyone to get to 12-under on Saturday, will follow the same strategy.
Thomas' historic round included nine birdies, including three straight to finish the front nine. Thomas, who had two bogeys on Saturday, birdied Nos. 15 and 17 before he hit a 3-wood on his approach shot on the par-5 18th hole to set up a short eagle putt that allowed him to get to 11-under.
But Thomas' lead, which sat at two shots after he eagled 18, lasted only temporarily as Fleetwood and Harman each birdied Nos. 14 and 15 to get to 12-under. But with a change in weather possibly coming, everyone that currently sits in championship contention understands that anything can happen come Sunday.
"It just depends on the weather," Harman said. "Someone could get out there early and shoot a low score. Justin did it today. It's out there for sure. There's just no telling how low. I could not be leading the golf tournament by the time I tee off tomorrow. That's a very real possibility."
Koepka shot 68.
NOTES: Patrick Reed, who shot a 65 on Saturday, wore a red, white and blue ensemble that included the blue pants he wore during the 2016 Ryder Cup, when the United States captured its first title since 2008. Asked if he had any say in what he wore, Reed said that his clothes are normally picked out for tournaments by his wife, his mother-in-law and sister-in-law. "You know, happy wife, happy life," Reed said. ... After establishing the U.S. Open scoring record, Justin Thomas -- who holds PGA marks for the best 36-hole, 54-hole and 72-hole records -- was asked if he considers himself the best player in the world. "(There's) no reason to answer that," said Thomas, who is currently ranked 13th in the world. "I can't win with the answer to that question."