UNIVERSITY PLACE, Wash. - Jason Day was simply zapped.

All the energy and effort needed to get through his remarkable third round at the U.S. Open caught up with the Australian while playing in the final group on Sunday.

Tired and drained, and still feeling the effects of the vertigo that caused him to collapse on the final hole of his second round, Day faded.

Understandable, and disappointing all the same.

"He was totally exhausted. He was exhausted yesterday," Day's caddie and longtime coach Colin Swatton said. "I'm not sure how much of yesterday took it out of him. I really don't. It's in the result. I don't know what to say. I'm obviously disappointed."

On another warm, grinding afternoon, Day couldn't muster up the energy needed for the final round. He closed with a 4-over 74 and finished at even-par for the tournament.

He made five bogeys and a double bogey, falling back into the pack with a rough three-hole stretch. Day missed a 12-foot birdie putt at No. 11 and a 6-footer at the 12th, then followed up with a double-bogey six at the uphill par-4 13th.

By the time he made birdie at No. 16, Day was five shots behind the leaders.

"I had a lot of in-between clubs and started feeling a lot better after the 12th hole. That was a plus," Day said. "I think I hit 13 greens and just didn't capitalize at all on the stuff that I had. It's unfortunate because I felt like I gave myself enough opportunities. Couple of putts, 11 and 12, go in and it's a different story, I feel different and opportunities come down the line. If you don't hole those, it doesn't go your way."

Afterward, Day said he likely would be "taking some time off" to get his health in order.

During the third round on Saturday, Swatton was constantly giving Day encouragement, although there were a handful of times when he believed Day was potentially ready to call it quits on the hilly layout. Day's vertigo returned near the end, even as he finished with birdies on three of his final four holes to move into a tie for the lead at 4 under.

There were less moments of concern about Day's health on Sunday, although Swatton said he clearly wasn't 100 per cent.

"Early in the round he said he wasn't feeling 100 per cent and as the round went on he sort of got into his groove a little bit," Swatton said.

Day's problem was simply not hitting the ball as well as he did 24 hours earlier. When Day missed, he put himself in bad positions to try and salvage par on the sloped greens. He missed the green badly on the 10th and needed a hand from Swatton to get out of a steep bunker.

Day also took five more putts than he did in the third round.

"He didn't hit as many fairways, missed the greens in some pretty bad places and didn't putt as good as yesterday," Swatton said.

Day still managed to finish in a tie for ninth for his eighth top-10 finish in a major since 2010 and his fourth top-10 in a U.S. Open.

"I was taken by the fact that so many people supported me," Day said. "I really made a lot of Jason Day fans out there this week, even though it didn't end up the way I wanted it to end up. I fought a good fight. And I think everybody that watched the telecast knows that I never gave up. It was a battle."