* Mahan crushes Yang 5&3
* Johnson thumps Molinari 7&5
* Woods loses one down to Watney (Updates at end of round)
By Mark Lamport-Stokes
MARANA, Arizona, Feb 23 (Reuters) - Tiger Woods tumbled out of the WGC-Accenture Match Play Championship on Thursday after fellow Americans Hunter Mahan and Dustin Johnson had eased into the third round with commanding victories.
Mahan became the first player to advance, crushing South Korean Yang Yong-eun 5&3, and Johnson followed with a 7&5 demolition of Italy's Francesco Molinari at Dove Mountain's Ritz-Carlton Golf Club.
Three-times champion Woods, however, went out in the second round for a third time at the elite World Golf Championships event, struggling on the greens as he lost one-down to compatriot Nick Watney.
"I'm very happy to move on," Watney told reporters after Woods had missed a six-foot birdie putt at the par-four 18th to keep the match alive. "I feel a bit fortunate, as well.
"We don't see him miss putts like that very often, and there were a few of them today. I don't think that this will be a day that either of us will look back on as far as putting goes."
Woods, who had been bidding for a first PGA Tour victory in over two years, took some comfort from the quality of his shot-making over the closing holes.
"I didn't miss a single shot coming in, which is good," the 14-times major champion said. "That was fun to hit the ball that well. Unfortunately I just didn't make a putt when I needed it."
British world number three Lee Westwood reached the third round for the first time in 12 appearances at the event, beating Swede Robert Karlsson 3&2, and fourth-ranked German Martin Kaymer edged past American David Toms two up.
Triple major winner Ernie Els, who had upset world number one and defending champion Luke Donald in the opening round, was ousted 5&4 by Swede Peter Hanson.
In blazing desert sunshine, Mahan birdied six of the first eight holes to go four up on Yang and recovered from bogeys at the ninth and 10th to seal the win on the 15th green.
"I was playing as well as I could, hitting fairways and greens, giving myself good looks," said Mahan, who will face U.S. Ryder Cup team mate Steve Stricker in Friday's third round.
"If you hit it good around here where these pins are and you get on the right level, you are going to have some putts, you are going to be able to make some putts. Today I was able to do that."
Stricker, champion in 2001 when the event was held in Australia, won a tight encounter with South African Louis Oosthuizen one up after sinking a 20-foot birdie putt at the 18th.
Johnson, who needed 20 holes to scrape past compatriot Jim Furyk in the opening round, never let up after seizing control against Molinari with four birdies in the first eight holes.
The match ended at the par-five 13th where the Italian parred and the big-hitting Johnson was just 10 feet from the hole in two shots.
"That momentum (from Wednesday) kind of carried over to today," Johnson said. "I got off to a good start and just played really solidly today."
John Senden, who putted well on Dove Mountain's tricky greens, upset fellow Australian Jason Day, the world number seven, 6&5.
"I had the pressure on him early," said Senden, who birdied two of the first four holes to go two up. "Then from there I wanted to keep focused and keep the quality of shots going on.
"And then I did that. And he sort of made the mistakes to force the match to go further and further my way."
In other matches, Masters champion Charl Schwartzel of South Africa lost to South Korea's Bae Sang-moon one-down and second-ranked Northern Irishman Rory Mcllroy advanced with a 3&2 win over Dane Anders Hansen. (Reporting by Mark Lamport-Stokes; Editing by Gene Cherry/Patrick Johnston)