Tiger Woods [Images], boosted by two monster birdie putts, grabbed the lead from overnight pacesetter Henrik Stenson in the Target World Challenge second round on Friday.

The world number one holed out from 40 feet at the ninth and from 50 feet at the 10th on his way to a four-under-par 68 at Sherwood Country Club.

That left him at eight-under 136, one ahead of Swede Stenson who carded an eventful 71.

U.S. Open champion Geoff Ogilvy of Australia returned a 70 to join American Chris DiMarco (68) in third place at six under with Britain's Paul Casey (70) a further stroke back in fifth.

"I drove it good again today but my iron game was not very precise and my speed on the greens was a little bit lacking," Woods told reporters after reeling off four birdies in a blemish-free display.

"I had another three-putt today and, overall, I've got a bit of room for improvement."

The 12-times major winner, champion here in 2001 and 2004, was frustrated he birdied only one of the five par-five holes on the undulating Jack Nicklaus-designed layout.

"I was in position to make birdies on a couple of them and I didn't do a very good job. I three-putted one and I missed a short putt there at 16," he said, referring to a five-footer that stayed out.

Woods, whose haul of eight PGA Tour victories this year included two majors, believes the 2006 season has been the worst of his career for three-putting.

"I've been very streaky with the putter this year," the 30-year-old American said. "The tournaments I've won I've putted very well. But I putted terribly on the Sunday at Augusta when I had a chance to win (the Masters)."

Tournament host Woods, bidding for his 11th title worldwide in 2006, began the day two strokes adrift of Stenson.

MAINTAINED ADVANTAGE

That soon became four after the Swede birdied the first two holes and Stenson maintained his advantage with 10 holes to play.

Woods made his move with long-range birdie putts on nine and 10 and the momentum ultimately shifted his way over the back nine.

"Those were two lucky breaks," he said of his successive birdies. "If you look at my speed on those putts, if they don't go in then I'm looking at probably two more three-putts."

"I've already got three this week, and that's three too many."

Although Stenson eagled the par-five 11th after hitting a fortunate second shot that bounced out of a bunker before finishing within eight feet of the flag, he double-bogeyed the par-three 12th after missing the green wildly to the right.

Woods rolled in a curling 10-foot birdie putt at the par-five 13th to tie Stenson for the lead and parred the last five holes to retain control of the tournament.

Despite a scrappy back nine that featured an eagle, a double-bogey, a birdie and two bogeys, Stenson was largely satisifed with his round.

"I got off to a good start today and then I played a few so-so shots," said the Swede, who won the Qatar Masters and the BMW [Images] International Open on the 2006 European Tour.

"Three bad shots cost me five strokes, otherwise it would have been a really good day."

World number four Adam Scott battled for the second day in a row, a dismal 80 dropping him into last place in the elite 16-man field at 11 over par.

Britain's Luke Donald, champion at Sherwood Country Club last year, was only five strokes better after returning a 74.