U.S. Ryder Cup captain Tom Lehman knocked out holder David Toms while Tiger Woods and Phil Mickelson were both ousted in Friday's third round on a day of upsets at the WGC-Accenture Match Play Championship.
World number one Woods, bidding for his third title of the year in four starts, struggled with his putting before losing a tight battle with Chad Campbell by a hole.
Left-hander Mickelson, who never led at any stage of his match with Britain's David Howell, went out 3&1 at a sun-drenched La Costa Resort and Spa.
There were also victories for Davis Love III, who beat fellow American Chris DiMarco 3&2, and Ireland's Padraig Harrington, who overcame Vijay Singh after 19 scrappy holes.
World number three Retief Goosen, who shaded Briton Luke Donald by a hole, was the only player among the tournament's top 10 seeds to book a place in the quarter-finals.
Lehman, world-ranked 37th, had trailed by one after five holes before fighting back against Toms, sealing a 4&3 win with a 15-foot birdie putt at the 15th.
Toms, who crushed compatriot DiMarco 6&5 in last year's final, narrowly missed a 14-footer to keep alive his eight-match winning streak in the event.
"It's always nice to win a match, especially against a player of the calibre of David Toms," a smiling Lehman told reporters.
"I think it would be safe to say that I have played steady golf all the way through to this point."
In the day's top tie, twice champion Woods battled to make putts on the front nine at La Costa and was three down with eight to play before mounting a rally.
He chipped in for an eagle-three from just off the edge of the green at the 11th and won the 12th with a par after Campbell missed the green to the left off the tee.
Campbell, who had lost in the third round in his two previous appearances at La Costa, countered with an eight-foot birdie putt at the par-four 13th to restore his two-hole advantage.
But he effectively gifted the next hole to Woods, finding thick rough to the left of the green with his approach and chunking his third shot into a greenside bunker on the way to a double-bogey six.
Back to one up, Campbell matched Woods with pars at the next three holes to stay in front with one to play.
After Campbell missed a birdie putt from 29 feet at the last, Woods had a chance to take the match into extra time but failed to sink his birdie attempt from 13 feet.
"I think to be able to come out and get that three-hole lead early on and also to be rebound from the things that happened on 11 and 12 is pretty huge for me," Campbell said.
"It was a great day but the tournament is not over yet just because you beat one guy."
A frustrated Woods said: "I thought I did pretty good today. I didn't make a bogey and lost the match. It's frustrating because I had my opportunities, I just didn't make anything on the greens.
"That's match play, you've got to make putts. All my opportunities to put pressure on him by making putts, I didn't do it. Consequently, he had free runs at putts and won the match."
Howell, the world number 15, holed four long birdie putts on his way to victory over hometown favourite Mickelson.
"I wasn't nervous today, strangely," the 30-year-old Englishman said. "I was comfortable last night, playing nicely.
"I guess it's a measure of where I stand in the world order nowadays. I'm a lot more comfortable in this situation."
Australia's Geoff Ogilvy eagled the 21st hole to outlast Canadian Mike Weir, who had led by four with four to play, and American Zach Johnson beat Shingo Katayama of Japan 4&3.