Tiger Woods' [Images] hopes of regaining the world number one ranking vanished when he went down 3 and 1 to Australian Nick O'Hern in the second round of the WGC-Accenture Match Play Championship on Friday.

The unheralded O'Hern's win ranked among the biggest upsets in the tournament's history, the left-hander ending the world number two's 13-match unbeaten streak at the La Costa Resort and Spa and his bid for an unprecedented third consecutive title here.

For the second consecutive week, Woods has let a chance to take back the number one ranking from Vijay Singh [Images] slip through his fingers.

The Fijian, who has never advanced past the second round in six visits to La Costa, left the door open for Woods by falling to American journeyman Jay Haas 3 & 2 in the second round.

Woods, who monopolised the world rankings for a record 264 successive weeks before being dislodged by Singh last September, needed to finish third or better to go back to the top of the pile.

Only once before in five previous starts had the 29-year-old American failed to reach at least the quarter-finals, losing to Peter O'Malley in the opening round in 2002.

DONALD BEATEN

Once again an Australian proved to be Woods's undoing, O'Hern going one up with a birdie at the second hole to seize control.

"In this game anything can happen," said O'Hern, who followed up by powering into the last eight with a 5 and 4 third-round victory over Briton Luke Donald.

"It was a matter of the least amount of mistakes. Tiger was just unlucky with some putts and I think that made the difference," the left-hander told reporters.

"I knew it was going to be tough but if I could keep playing solid I knew I would have a chance, and he would have to play some really good golf to beat me.

"A good friend of mine, Pete O'Malley, beat him a few years ago so I knew he wasn't unbeatable."

Woods's form on the greens again proved his downfall, the eight-times major winner grimacing several times as he watched putts lip the hole.

"With the greens not being so good, it's hard," said Woods. "I hit a lot of good putts that didn't go in, a lot of lip outs.

"I hit good putts and you could see them bounce a little bit. You've got to hit and hope. I hit good putts where I was looking.

"That was certainly the difference in winning and losing a match. Nick made all the putts that he was in position to make and I didn't."