Oosthuizen, who finished second in the US Open in 2015 and lost a play-off for the Open a month later, had to settle for a 68 to finish four under par. Harman had back-to-back birdies on 14 and 15 before closing out with three straight pars to take over the lead.
But only for a couple minutes.
Thomas became the first man to shoot nine-under score in the history of the US Open.
U.S. Open, final round, Fox, 8 a.m.
And the prime beneficiary was Thomas, who catapulted up the leaderboard with his record-breaking nine-under-par 63.
Another big mover was Patrick Reed, who looked like he might have posted the round of the tournament shooting a 7-under 65 early on Saturday, before Thomas' posted his insane good score later in the day.
In the process, Thomas had moved up 22 spots on Moving Day, which is akin to moving from MA to Maui.
Thomas became the fifth player to shoot 63 in the U.S. Open, and the first with a score of 9 under.
Harman, bidding to become the first left-hander to win a US Open, is a victor on the PGA Tour this year while Thomas is the world number 13, a three-time victor this season and a member of the exclusive "59" club after breaking 60 at the Sony Open this year.
Fleetwood's 4-under-par 68 Saturday left him one shot off the lead. Or at your home course.
Fowler pitched the ball to about 18 feet, then missed the next putt on his way to a bogey. He was 10 under, only two shots behind.
Fowler came back to birdie the par-3 ninth to get back to one shot back.
Spieth had five birdies and two bogeys in his final round. And then my expectations were lowered on the greens given the conditions. About all that saved Erin Hills from another onslaught was a forecast for the strongest wind of the week.
The 26-year-old Reed had eight birdies and one bogey.
Up to that point, Fleetwood pretty much couldn't find trouble if he tried.
Charley Hoffman is all by himself on top of the U.S. Open - for now.
Koepka birdied his first two holes to get to 13 under.
"This is my first time in contention in a major, so whatever happens I'll be doing my best and seeing how well I can finish".
Steve Stricker is soaking up the warmest ovations of the third round in his home state of Wisconsin. His 4-under 68 included six birdies - Nos.
The putt ran past the hole and settled at the bottom of a collection area 70 feet away. He shot a 69 and was at 2-under 214. "But it isn't a U.S. Open course that I'm familiar with the way it was set up". He just has to listen to the crowd.
Tom Kite knows a little something about hard conditions for the final round of the U.S. Open.
The one thing all of these golfers have in common? He grabbed his putter and pointed it out to his left just as the ball dropped into the cup.
"It was an awesome day", Thomas said.
Scottie Scheffler is the low amateur for this year's U.S. Open. Thomas, Brooks Koepka and Tommy Fleetwood were one shot back. He has birdied three of his last four holes.
Champ and Scottie Scheffler are tied at 1 under. Champ tees off later Saturday.
Spieth had a nice day considering how the winds have picked up at Erin Hills. 1, 7 and 9 on the front nine and three in a row on Nos.
The flag commemorates the late Arnold Palmer's win at the 1960 U.S. Open at Cherry Hills.
Not bad for a guy who made the cut on the number.
"It's going to be a really cool day for someone tomorrow", Fowler said. There have been a pair of 65s, and Brian Harman holds the 54-hole lead at 12-under.
But that's not all that makes the possibilities so limitless Saturday.
Harman is playing in just his eighth major, and it's only the third time he has made the cut.
Now consider that the largest 36-hole comeback in U.S. Open history was 11 shots by Lou Graham in 1975.