Tiger Woods is hoping to put a terrible fourth day and a sore knee behind him when he takes on Rocco Mediate in an 18-hole play-off to decide who will win the 108th US Open.

The world number one sunk a 12-foot putt for birdie at the 18th to move level with his fellow American at the top of the leaderboard on one-under after 72 holes.

A fifth round will now be needed on Monday to decide the winner, meaning Woods will have to put his injured knee through further pain if he is to win a 14th Major.

However, the 32-year-old was more concerned with his poor play than his physical status, admitting he was just glad to have a chance of still winning the tournament.

"I hit it terrible today, just a terrible day of ball striking," he said. "But I hung in there, scrapped around and gave myself a chance.

On the knee injury, Woods added: "It was pretty sore. I took some things to relieve that, and now here we are. At least I've got a chance."

After a difficult round, the two-time US Open champion showed nerves of steel to roll in the final stroke of the day to finish with a score of 71.

"That's actually one of the worst parts of the green, it's so bumpy down there," he said of his putt on the 18th.

"I told myself it was two and a half balls outside to the right, but make sure you stay committed to it. And I did.

"I hit it good. It took forever to break, but it finally snuck in there at the end."

Woods has twice before needed a play-off to win a Major. He beat Bob May at the PGA Championship at Valhalla in 2000 and then saw off the challenge of Chris DiMarco at The Masters five years later.

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