World number one Tiger Woods suffered a shock first-round exit to fellow American Shaun Micheel at the World Match Play Championship at Wentworth.
Woods, winner of his last five tournaments, was below his best and lost 4&3 to the former USPGA champion.
Six of the top eight seeds lost, with world number two Jim Furyk beaten 4&3 by Robert Karlsson and six-time winner Ernie Els beaten 2&1 by Angel Cabrera.
But Colin Montgomerie, Paul Casey, Luke Donald and Michael Campbell advanced.
Defending champion Campbell turned around an early two-hole deficit to win 3&1 against Englishman Simon Khan.
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"I managed just to hang on," said Montgomerie. "I was never down all day, but he's a tough competitor."
Paul Casey, on his debut in the event, recovered from a two-hole deficit after 11 holes to claim a fine 6&4 victory over South African Retief Goosen.
"I am ecstatic," said Casey, who enjoyed a run of four birdies and an eagle in six holes after drawing all square at lunch.
"Retief is a tough guy to beat and I haven't played in a 36-hole match for a long time, probably as an amateur."
He now faces Canada's Mike Weir, who upset world number five Adam Scott 3&2.
Donald looked set for an easy win over Tim Clark before the South African fought back to square the match after 33 holes.
"Tiger has been playing some great golf and will continue to do that"
"If I had a choice I would probably have chosen to play against Shaun, but he must have played great to beat Tiger and I am sure he will be on a big high," Donald said.
Micheel himself was not so impressed with his own effort, but understandably delighted with a rare win over the world number one.
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"I don't think either of us played played really well," said Micheel, whose hat-trick of birdies from the third hole sparked his victory. "I played OK but not as well as I would have liked.
"I have finished second to Tiger more times than he has finished second to me. But he has been playing some great golf and will continue to do that."
Woods was undone by uncharacteristically poor putting, missing a putt from less than three feet at the ninth.
"I felt like I hit the ball pretty decent all day but I just didn't make any putts," said the world number one.
"I had my chances but had a hard time with my pace on the greens."
First-round results at Wentworth:
Michael Campbell (1) beat Simon Khan (16) 3&1
Colin Montgomerie (9) beat David Howell (8) 1 up
Paul Casey (12) beat Retief Goosen (5) 6&4
Mike Weir (13) beat Adam Scott (4) 3&2
Robert Karlsson (14) beat Jim Furyk (3) 4&3
Angel Cabrera (11) beat Ernie Els (6) 2&1
Luke Donald (7) beat Tim Clark (10) 2 up
Shaun Micheel (15) beat Tiger Woods (2) 4&3
Friday's quarter-final tee-off times:
0800 and 1245 Michael Campbell (1) v Colin Montgomerie (9)
0815 and 1300 Paul Casey (12) v Mike Weir (13)
0830 and 1315 Robert Karlsson (14) v Angel Cabrera (11)
0845 and 1330 Luke Donald (7) v Shaun Micheel (15)