Brian Harman (five-under 67) of the United States ended the third round of the US Open at Erin Hills, Wisconsin, on Saturday atop the leaderboard on 12-under 204 total, one shot ahead of compatriots Justin Thomas (63), and Brooks Koepka (68) and England's Tommy Fleetwood (68).
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.