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Charlie Riedel, AP
Jordan Spieth watches his tee shot on the 10th hole during the third round of the U.S. Open golf tournament at Chambers Bay on Saturday, June 20, 2015 in University Place, Wash. (AP Photo/Charlie Riedel)

UNIVERSITY PLACE, Wash. — Everyone will be chasing four front-runners in the final round of the U.S. Open.

Masters champion Jordan Spieth missed a 12-footer for birdie on the finishing hole Saturday, leaving him 4 under for the championship. He is tied with Dustin Johnson, Branden Grace and Jason Day, who overcame a bout of vertigo to shoot a memorable 2-under 68 at Chambers Bay.

Spieth is trying to become the first player since Tiger Woods in 2002 to win the first two majors of the year. He shot a 1-over 71 in difficult conditions.

Louis Oosthuizen shot the day's best round, a 4-under 66. He is at 1 under along with J.B. Holmes, Cameron Smith and Shane Lowry. Six others are 1 over.

Day crashed to the ground as he finished his second round Friday and later was diagnosed with vertigo, which had caused him to withdraw from a tournament last year. Even though he was three shots out of the lead, he wasn't sure he would be able to play. Still groggy from medication, and coping with symptoms of vertigo on a long, brutal afternoon at Chambers Bay, the Australian fought his way to the top.

He used the slopes for a short birdie on the 15th. He made a 15-foot birdie on the 17th. And he brought the fans in that massive grandstand to their feet when he holed a 5-foot birdie putt on the 18th.

Day chose not to speak to reporters, wanting to get back to his room to rest.

"I didn't feel that great coming out early," Day said to a USGA official. "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. But then it kind of came back — the vertigo came back a little bit on the 13th tee box, and then felt nauseous all day. I started shaking on 16 tee box and then just tried to get it in, really. Just wanted to get it in."

His caddie and coach, Colin Swatton, said Day considered quitting three times.

"I think the goal was just to go through today and see how it goes," Day said.

The conditions were the toughest they have been all week, no surprise for Saturday at a U.S. Open.

Spieth raced out to a two-shot lead with a pair of long birdie putts early in his round, only to make a pair of three-putt bogeys that had him slapping his knee in disgust. The Masters champion rallied with two key par saves and a birdie on the 15th.

Johnson built a two-shot lead, only to give it back with a double bogey on the 13th hole with a poor second shot into the bunker. Grace had three bogeys in a five-hole stretch and rejoined the leaders with a birdie on the 15th.

But the big surprise was Day, who moved slowly even to stick a tee in the ground.

Louis Oosthuizen, meanwhile, set himself up for a shot at U.S. Open history. No one since World War II has ever shot 77 in the first round of the U.S. Open and gone on to win. Oosthuizen was part of that horror show with Tiger Woods (80) and Rickie Fowler (81) in the opening round. He figured he would be watching the weekend at his home in Florida. Instead, he shot 66 to make the cut. And then the South African shot another 66 on Saturday and was at 1-under 209.

Cameron Smith of Australian had a 69 and joined Oosthuizen at 209, along with Shane Lowry of Ireland (70) and J.B. Holmes (71).

The number of players under par kept dropping — 25 after the first day, 16 after the second. As the third round headed into the final hour, only nine players remained under par. And the yellow-and-brown color of the grass was the best indication that those numbers were likely to fall even more.

Rory McIlroy was losing hope in this major. He shot a 70 and was at 4-over 214. Phil Mickelson, meanwhile, lost another bid at the career Grand Slam with a 77 that put him at 10-over 220.