(Reuters) - The sheer lottery of the WGC-Accenture Match Play Championship was again front and center on Thursday as top seed Henrik Stenson of Sweden and fourth-seeded Northern Irishman Rory McIlroy were both eliminated in the second round.
Stenson, the 2007 champion, never led before going down 4&3 to South African Louis Oosthuizen while McIlroy lost a see-sawing encounter with American Harris English after 19 holes at Dove Mountain.
McIlroy, beaten by American Hunter Mahan in the 2012 final, had clawed his way back from two down after 13 holes to edge one up after 16 on another breezy day of dazzling sunshine in Arizona's high desert.
However, English levelled the match with a birdie at the par-four 17th and sealed victory after his opponent made a compete hash of the 19th.
"Obviously a little bit disappointed with how I finished," McIlroy told reporters. "Being two down with five to go, playing the last five holes like I did, I was happy about that.
"I didn't hit the greatest drive off the 19th and got a pretty bad lie in the rough. It was just unfortunate. I played pretty well for the most part.
"But, you know, he played really solid today and didn't really do much wrong, didn't really give me anything. So the more consistent player won at the end of the day."
English will next face Jim Furyk, the PGA Tour veteran having beaten former Masters champion Charl Schwartzel of South Africa 3&2.
Oosthuizen won three of the first four holes against a sub-par Stenson and maintained control before ending the match with a birdie at the par-four 15th.
"I played pretty solid today," Oosthuizen said. "I just kept it together. Henrik didn't start very well and I made an early lead.
"I just played solid and made nice putts on the back nine. I'm playing well. I'm just trying to keep the ball in play so that I'm in every hole I'm playing."
Rickie Fowler continued his giant-killing ways with a one-up win over in-form fellow American Jimmy Walker and will next meet Spaniard Sergio Garcia, who beat good friend Bill Haas of the United States 3&1.
Fowler came from one down with three holes to play, sealing his second win of the week with a birdie on 16 followed by well executed par saves on 17 and 18.
"I told my caddie, 'Joe, let's try and birdie the last three, make some good swings'," Fowler said. "I didn't birdie 17 and 18, but I made two really good putts along with the birdie putt on 16."
Fowler, who upset match play expert and 2010 champion Ian Poulter in the opening round, was delighted to add the scalp of Walker, who has already won three times on the 2013-14 PGA Tour.
"He's on top of his game," Fowler said. "I knew coming in today that even if he didn't bring his 'A' game, he was going to be tough to beat. Definitely nice to come out on top."
Garcia, who had battled past Australian Marc Leishman after 22 holes in his opening match, was two down after seven holes but sparked his fightback with an eagle at the eighth before taking control with three birdies after the turn.
American Jordan Spieth, the 2013 PGA Tour rookie of the year, was always in command against Denmark's Thomas Bjorn before wrapping up a comfortable 5&4 victory.
Frenchman Victor Dubuisson, a debutant at Dove Mountain this week, never trailed on the way to a 3&1 win against Swede Peter Hanson.
Dubuisson will next face former Masters champion Bubba Watson, who beat Swede Jonas Blixt two up.
Defending champion Matt Kuchar won a tight contest against fellow American Ryan Moore one up while Australian Jason Day battled back from three down after 10 holes to scrape past American Billy Horschel after 22 holes.
(Reporting by Mark Lamport-Stokes in Los Angeles; Editing by John O'Brien)