(CNN)A visibly struggling Jason Day overcame the lingering effects of vertigo to charge up the field and tie for the lead at the third round of the U.S. Open.
The Australian collapsed on the ninth hole of the Chambers Bay Golf Course Friday and looked to be struggling with dizziness on several occasions Saturday.
But five birdies on the back nine canceled out three earlier bogies to ensure a two-under-par round of 68 leaves Day tied atop the leaderboard alongside Dustin Johnson, Branden Grace and Jordan Spieth.
Day even fumbled the ball as he tried to place it on the green for his final putt of the day and looked like he was leaning on caddy Colin Swatton to remain upright.
"I felt nauseous all day" said Day afterwards in comments carried by the tournament website.
"Last year, I (withdrew) after I had vertigo and this one was worse. I think the goal was just to go through today and see how it goes," he added before leaving to receive medical attention and rest ahead of Sunday's final round.
Swatton, who doubles up as Day's swing coach, was effusive on his player's performance.
"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."
"He just put his head down and kept walking one foot in front of the other. It was pretty impressive."
The leading group is three shots clear of a chasing pack that includes former British Open champion Louis Oosthuizen, Cameron Smith, Shane Lowry and J.B. Holmes.
Holmes underwent brain surgery after struggling with symptoms including vertigo for several months in 2011 and offered an insight into Day's predicament.
"I had those types of symptoms. It was very difficult sometimes to even play," he said.
"In one way it kind of makes it easier because you're trying to get to the next shot and you're staying very present. Whether he's feeling good or great, it's great playing."