Heroic Jason Day shares lead after third round despite dizziness

Even though Day's round will be long remembered, there is still another chapter to be written in the 115th U.S. Open with Americans Jordan Spieth and Dustin Johnson and South African Branden Grace all level on four-under 206 going into Sunday.

Day had collapsed on his final hole on Friday and had to be helped from the course by medics after he collapsed again when he completed his round three shots off the lead.

There was worry the world number 10 would have to withdraw but he dug deep and on Saturday was back on the first tee.

Looking drained, Day shot a two-under 68 highlighted by a brilliant back nine that featured five birdies, including three over his four closing holes.

His storming finish earned him a share of the lead and a rousing standing ovation from the 6,000 fans packed into the 18th hole grandstands.

Day took only a moment to savour the applause as he gingerly made his way to a waiting van where he slumped into the back seat with closed eyes and laid his head on the back rest.

"Last year I didn't play the round after I had vertigo and this one was worse," Day told reporters. "I think the goal was just to go through today and see how it goes."

Day's effort dominated another dramatic afternoon on the links-style layout that saw five different names at the top of the leaderboard and an assortment of brilliant and bewildering shots.

Masters champion Spieth and his American Ryder Cup team mate Patrick Reed began the day with a one-shot lead but as the sun set into Puget Sound the leaderboard had a very different look.

One of the longest courses ever for a golf major, Chambers Bay was tailor-made for the big-hitting Johnson, who muscled his way to the top with an even-par 70 while Grace, a six-time winner on the European Tour, also had a 70.

With its picture postcard vistas, Chambers Bay may have an attractive look but it has been widely criticised by golfers and commentators with the attacks growing louder with each day.

Most of the grumbling has been directed at the bumpy and undulating greens, but Spieth proved they can be conquered as he rolled in a 38-foot birdie putt at the second to move two ahead.

The world number two continued to wield a hot putter, draining a 40-footer for birdie at the third to open up a three-shot cushion.

But even the best putter in the game would have his problems with the controversial greens and Spieth's first wobble came at the fourth when he three-putted from 30 feet for his first bogey.

That was followed by another at the fifth and suddenly Spieth's three-shot advantage had vanished, leaving him to scramble his way to a 71.

"I knew that even par was a really good score starting the day, but when I get to seven-under for the tournament I don't want to finish at four-under, no matter where you're playing," said Spieth, who will try to become just the sixth player to win the Masters and U.S. Open in the same year.

"I had four three-putts today and that's going to happen out here but two of them are unforced and shouldn't have happened."