Jason Day's effort was hailed as superhuman as he defied debilitating vertigo to capture a share of the US Open lead going into the final round.
Still battling the problem which caused him to collapse on the course on Friday, Day put together a brilliant two-under-par 68 on the brutally tough Chambers Bay layout on Saturday.
The world No.10 ranked Australian shares the lead with Americans Dustin Johnson (70) and Jordan Spieth (71) and South African Branden Grace (70), with the quartet enjoying a three-shot buffer to their nearest challengers.
Only Louis Oosthuizen's 66 topped Day's score and the Queenslander's long-time caddie, coach and father figure Col Swatton was in awe of his 27-year-old charge's achievement.
"That was superhuman effort. That was the greatest round I've ever watched," said Swatton.
"They're going to make a movie about that round. It was pretty impressive, it was up there with Tiger Woods playing with a broken leg at the US Open (in 2008)."
Searching for his maiden major title after coming close on several occasions, Day will play in the final group with Johnson.
He already has two runner-ups and a fourth in just four previous US Open starts and also has a runner-up and a third place finish at the Masters.
Swatton revealed Day came to withdrawing, including three times on the back nine when he rallied instead, producing three birdies in his final four holes.
"I said you've got the heart of a lion. You're going to show the world today you're going to be the greatest you can be," Swatton said.
"He said, 'let's do it' and he just put his head down and kept walking one foot in front of the other."
Evoking memories of Ken Venturi's 1964 US Open win when he battled heat exhaustion to claim the trophy, Day has become a huge crowd favourite and received loud applause around the course.
The 27-year-old Queenslander has struggled with his health this year and also pulled out of last August's World Golf Championship Bridgestone Invitational and this year's Byron Nelson Championship with a similar vertigo problem.
After collapsing on his final hole of his second round on Friday and subsequently being diagnosed with benign positional vertigo, Day wasn't even a certainty to tee it up Saturday.
Just a few hours before his tee time he was still lying down in his motorhome unsure whether he could play.
The 27-year-old was noticeably trying to keep his head level to prevent another episode - struggling to tee his ball up and retrieve it from the cup all day.
Swatton offered to do those things but Day refused to be seen as incapable.
"I didn't feel that great coming out early, and then I felt pretty groggy on the front nine just from the drugs that I had in my system, then kind of flushed that out on the back nine," said Day.
"But it (vertigo) kind of came back. The vertigo came back a little bit on the 13th tee box, and then I felt nauseous all day.
"I started shaking on 16 tee box and then I just tried to get it in, really. I just wanted to get in."
Despite his travails and the odds against him, Swatton was confident he could not only play on Sunday but triumph.
"Of course he can win. To win a major healthy is difficult enough, to win one not 100 per cent is even more difficult but you've seen what he's capable of.
"It's going to be a tough day tomorrow but he will give it a good crack. "
Day's young countryman Cameron Smith, on debut in the majors, shot a brilliant 69 to move to one-under and a tie for fifth.
A top five finish would get him a US PGA Tour card.
Adam Scott shot a 72 to be tied 19th at three-over, John Senden is four-over, Geoff Ogilvy six over and Marcus Fraser nine over.
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