Thomas became the first man to shoot nine-under score in the history of the US Open. His third round featured six birdies and an eagle (par-five 18th) and two bogeys.
Harman, who won the Wells Fargo championship last month, continued in his rich vein of form on Saturday, sinking six birdies.
"It's the best I've struck the ball in a long time. And my short game is pretty good. I've been putting it pretty good. So I'm excited about all those things," Harman told usopen.com.
"Obviously, I have no idea what tomorrow holds, but I'm more motivated by the way that I'm striking the ball."
This is his third appearance at the US Open, and the first time he has made the cut.
England's Fleetwood had led until the final hole, when only his third bogey of the week meant he relinquished the lead to 30-year-old Harman, leaving himself tied with Koepka and Thomas.
In addition to being the first to register nine-under score, Thomas also became just the fifth man in the history of the US Open to score 63.
"I'm just so excited to give myself a great chance to win this golf tournament. I feel like my game has been good enough to compete in the majors this year," Thomas said.
Rickie Fowler carded 68 to take his total to 10-under 206. One shot behind him was South Korea's Si Woo Kim, who posted a 68 in the penultimate round.
Patrick Reed (65), Russell Henley (67) and Charley Hoffman (68) shared the seventh spot at eight-under 208 total.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
Doraiah Chowdary Vundavally is a Software engineer at VTech . He is the news editor of SocialNews.XYZ and Freelance writer-contributes Telugu and English Columns on Films, Politics, and Gossips. He is the primary contributor for South Cinema Section of SocialNews.XYZ. His mission is to help to develop SocialNews.XYZ into a News website that has no bias or judgement towards any.
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