Luke Donald's defence of his WGC-Accenture Match Play Championship title lasted just 14 holes as he was thrashed 5&4 by Ernie Els in Tucson.
The South African, who squeezed into the field when Phil Mickelson pulled out, took full advantage of some erratic play from the out-of-sorts world No 1 on a course he dominated last year.
Donald gave away the third hole when he twice found water, but he pulled level with a birdie at the eighth before the Englishman's all-round game started to disintegrate.
Wayward iron play and a lack of confidence on the greens hit Donald hard as Els stormed four ahead in the space of five holes around the turn.
Els closed out a surprise victory with his fourth birdie at the 14th, and Donald was at a loss to explain his woeful performance after becoming only the third top seed to fall at the first hurdle.
"Not sure where to start - I just didn't play well," said Donald. "It's disappointing. I've worked hard and to lose control of the ball is frustrating.
"I felt pretty good about where I was and I'm not sure what happened. Hopefully just one of those bad days."
But Lee Westwood salvaged some of England's dented pride as he followed Robert Rock into the second round, rolling in six birdies in a 3&1 win over Nicolas Colsaerts.
"I didn't make a bogey and it was a good match," said Westwood, who faces Robert Karlsson in the second round. "You can't cruise your way into the tournament, as I do in a lot of them."
Draw for second round:
BOBBY JONES
(64) Ernie Els v (33) Peter Hanson
(49) Kyle Stanley v (17) Brandt Snedeker
(57) Robert Rock v (40) Mark Wilson
(9) Dustin Johnson v (41) Francesco Molinari
BEN HOGAN
(4) Martin Kaymer v (29) David Toms
(13) Matt Kuchar v (20) Bubba Watson
(5) Steve Stricker v (28) Louis Oosthuizen
(53) YE Yang v (21) Hunter Mahan
GARY PLAYER
(2) Rory McIlroy v (34) Anders Hansen
(50) Miguel Angel Jimenez v (18) Keegan Bradley
(7) Jason Day v (39) John Senden
(10) Charl Schwartzel v (42) Bae Sang-moon
SAM SNEAD
(3) Lee Westwood v (30) Robert Karlsson
(14) Nick Watney v (19) Tiger Woods
(59) Matteo Manassero v (38) Martin Laird
(54) Ryo Ishikawa v (43) Paul Lawrie.
