American Matt Kuchar became the first player to reach the quarter-finals of the WGC-Accenture Match Play Championship when he ousted German world No 4 Martin Kaymer 4 and 3 on Friday.
Kuchar came from one down after three holes with a rock-solid performance at Dove Mountain's Ritz-Carlton Golf Club as Kaymer, beaten by Luke Donald in last year's final, perpetually struggled on the tricky greens.
World No 14 Kuchar struck his tee shot to within two feet of the cup at the par-three sixth for a conceded birdie to go one up before his lead was doubled when Kaymer three-putted from six feet to bogey the par-five eighth.
The consistent American then birdied the 10th and 11th to go four up before sealing the win with a matching par on the 15th green.
Soon after, Hunter Mahan completed another upset when he stunned US Ryder Cup team mate and world number five Steve Stricker 4 and 3 after a sizzling display in the Sonoran desert.
In-form Mahan piled up nine birdies in dazzling sunshine, the last of them conceded by Stricker from just two feet at the driveable par-four 15th to end the match.
British world No 3 Lee Westwood was three up on American Nick Watney after 14 holes while second-ranked Northern Irishman Rory McIlroy was three up on Spaniard Miguel Angel Jimenez after 10.
In other matches, Swede Peter Hanson was two up on American Brandt Snedeker after 12 holes and Mark Wilson was four up on fellow American Dustin Johnson, also after 12.
Tiger Woods tumbled out of the tournament in the second round for a third time, 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."