Top seed Luke Donald crashed out of the WGC-Accenture Match Play Championship on Wednesday, losing 5&4 to late entry Ernie Els, while Tiger Woods scraped through into the second round.
Once again the elite World Golf Championships event lived up to its reputation for wild unpredictability and there were 15 upsets from the 32 matches at Dove Mountain's Ritz-Carlton Golf Club in Marana, Arizona.
Donald won last year's title with an imperious display, never trailing in any of his six matches, but he struggled against South African Els.
Triple major winner Els made the most of an error-prone performance by the British world No. 1 and sealed victory when he sank a 10-foot birdie putt at the par-four 14th.
"I'm not sure where to start," a subdued Donald, who became only the third top seed to lose in the event's opening round, told reporters.
"I just didn't play very well. It's disappointing. I gave away too many holes and made too many mistakes.
"You can't do that in match play against anyone, let alone Ernie."
The lowest-ranked player in the elite field of 64, former world No. 1 Els was gifted a spot at Dove Mountain when Phil Mickelson withdrew to spend time with his family.
"There's always hype when the No. 1 player is playing the No. 64 seed," said Els.
"But Luke and I took it for what it was. I think he didn't want to play me and I sure as hell didn't want to play him in the first round, but that's the way it worked out."
While three-time winner Woods battled through one up against Spaniard Gonzalo Fernandez-Castano, Charl Schwartzel and Bae Sang-moon won their opening matches in comfort.
Masters champion Schwartzel of South Africa eased past big-hitting American Gary Woodland 4&2 and South Korean Bae upset Britain's Ian Poulter, the 2010 champion, 4&3.
Northern Ireland's Rory McIlroy survived a late wobble to beat South African George Coetzee two up, Lee Westwood beat Belgian Nicolas Colsaerts 3&1 and German Martin Kaymer advanced with a 4&2 win over Australian left-hander Greg Chalmers.
Woods, winner of this event in 2003, 2004 and 2008, was two down to Fernandez-Castano after two holes but finally ended a wildly fluctuating encounter with an eight-foot par putt at the 18th.
"We both made our share of mistakes, there's no doubt about that, but somehow I was able to move on," Woods said.