UNIVERSITY PLACE, Wash. - Never has Jason Day played so well feeling so miserable.

"I said to him 'They might make a movie about that round.' It was pretty impressive," Day's caddie Colin Swatton said. "It was up there with Tiger Woods playing with a broken leg and winning the U.S. Open. It's pretty impressive."

A day after the Australian collapsed at the end of his round due to vertigo, Day shot 68 in the third round of the U.S. Open on Saturday, overcoming heat, fatigue and continued bouts of dizziness to post one of the best rounds of the day.

Only Louis Oosthuizen's 66 topped Day, barely 24 hours after he needed medical attention. Day immediately went to his trailer to rest after zooming up the leaderboard thanks to five birdies on his final nine holes that had Chambers Bay roaring with support.

By the end of the third round, Day was in a four-way tie for the lead and in the final group on Sunday.

"The vertigo came back a little bit on the 13th tee box, and then felt nauseous all day," Day said. "I started shaking on 16 tee box and then just tried to get it in, really. Just wanted to get it in."

Swatton had no concern about how Day was on the practice range after Day hit balls for 40 minutes. But he thought Day might not be able to continue after making the climb up to the fourth hole, one of the more difficult hikes on the course. There was also the vertical challenge of the seventh hole. Swatton joked after Day made par, "It's all downhill from here."

"I said, 'You've got the heart of a lion, you get to show the world today you get to be the greatest you can be and look, let's do it.' And he just put his head down and kept walking one foot in front of the other," Swatton said.

Day was a universal fan favourite. Cheers of "Come on Jason," followed him to every hole with one yell of "Stay strong brother," in a Hulk Hogan voice as he walked up the 11th fairway.

Even as Day charged on the back nine, the struggle grew. Everything was measured, from putting the tee in the ground, to his steps down the fairway.

Yet the more Day fatigued, the better his score.

"He had moments when he felt really good and then he had moments when he didn't feel so good. But that was throughout the whole round," Swatton said. "The score didn't reflect anything. . There was no mention of where he was on the leaderboard or anything like that. It was just, next hole, next shot."

Day's start was similar to his health: Shaky. He bogeyed two of his first four holes, but started his rally when nearly dropped an 18-foot birdie putt on No. 9, the hole he collapsed on Friday.

Day's back nine run began with a 5-foot birdie on No. 10 after a perfect second shot. He bogeyed the 11th, but made birdie on the drivable par 4 12th and walked away with pars on the 533-yard 13th and 534-yard 14th, both coming because of Day's short game.

On the 15th, playing 256 yards on Saturday, Day hit a 5-iron and used the slope of the green as a backstop, his ball settling 8 feet away. Day made the putt to get back even for his round and dropped another short putt for birdie on the 17th, eliciting one of the loudest roars from the crowd.

Day felt perhaps his worst on the 18th. He got a lucky break when his wayward tee shot hit a hospitality tent and bounced back into play. His third shot left him 6 feet for birdie and an unforgettable round.

"I had a feeling he was going to make that," Swatton said.