Tiger Woods [Images], who has nursed a painful knee all week, rolled in a 15-foot birdie putt at the last on Sunday to join fellow American Rocco Mediate in an 18-hole playoff for the 108th US Open.

Heavy favourite to win his 14th major title after going into the final round a stroke in front of the chasing pack, Woods looked skywards and pumped his fists after the putt dropped.

"It was a little wobbly down there," the world number one told reporters of his putt, the first of any distance he made on the day as the greens became increasingly bumpy.

"The putt was probably about two-and-a-half balls outside right and the green wasn't very smooth. I kept telling myself make a pure stroke. I hit it exactly where I wanted to."

As for his knee pain during the round, Woods said: "Did it get better? No. I took some things to relieve that so I feel a bit better now."

Mediate, who won the last of his four PGA Tour titles in 2002, had led by a shot with one hole to play.

"You can't ever expect him to miss," the 45-year-old and world number 157 said of Woods's last-gasp putt which curled in from the right edge. "I will just have to get ready for a battle royale tomorrow."

The pair finished the 72 regulation holes at one-under-par 283 on a difficult afternoon of scoring on the South Course at Torrey Pines in the final round.

Twice champion Woods, who has never lost a major when holding at least a share of the lead after 54 holes, closed with a two-over 73 after Mediate had signed off with a 71.

The pair will return on Monday for the playoff, starting at 0900 local (1600 GMT).

Britain's Lee Westwood, aiming to become the first European winner since fellow Englishman Tony Jacklin in 1970, had to settle for third place at level par after carding a 73.

BIRDIE ATTEMPT

Westwood, who had led by one with nine holes to play, also had a chance of joining the playoff but missed his birdie attempt from 18 feet on the 18th green.

It is the first time the US Open will be decided in extra time since South African Retief Goosen beat American Mark Brooks at Southern Hills in 2001.

"I'm looking forward to it, I've never been in this position before in a US Open," said Woods, whose only playoff victories in majors came at the 2000 PGA Championship and the 2005 Masters.

Mediate, Woods and Westwood each held the outright lead as the final round unfolded in scrappy fashion.

Woods, US Open champion in 2000 and 2002, made an ugly start by dropping three shots in the first two holes.

He double-bogeyed the first after pulling his tee shot left of the cart path and hitting trees with his second and third shots before three-putting for bogey at the par-four second.

After parring the next six holes, he picked up his first shot at the par-five ninth where he reached the green in two.

Woods, who experienced jabs of pain during the week after having knee surgery two months ago, finally regained the lead with a birdie at the 11th.

He coolly rolled in the putt to edge one stroke clear at two under, sparking a huge roar from the gallery.

However, he surrendered the initiative by bogeying the par-five 13th where he had to take a penalty drop.

Woods, who had eagled the hole in the previous two rounds, reached the elevated green with his fourth and two-putted for a six to slip back to one under.

Mediate edged ahead after collecting his third birdie of the round at the 267-yard 14th where he drove into a greenside bunker and got up and down.

Although he bogeyed the 15th to slip back to one under, Woods faltered at the same hole after missing the fairway to the right before forcing the playoff at the last.