LOS ANGELES (AFP) - Defending champion Rory McIlroy advanced to the knockout stage of the WGC Match Play on Friday after winning a nervy sudden death play-off against Kevin Na.
McIlroy progressed to a last 16 showdown with in-form American Zach Johnson after his winner-take-all Group 3 clash with Na finished all square after 18 holes at the Austin Country Club in Texas.
After both players parred the first sudden death hole, McIlroy was handed the initiative when Na sent his drive into a hazard on the second.
McIlroy comfortably took care of business to par while Na made bogey.
"It was tough. All three of my matches this week have been pretty tough," said a relieved McIlroy after the win.
"I didn't get off to the best of starts again, but I found my rhythm in the middle of the round and started to make some birdies. I had a couple of chances to maybe finish him in regulation.
"It took a mistake from him to get me over the line and obviously I'm just happy to be in the weekend."
McIlroy said he was looking forward to locking horns with 14th seed Johnson, who reached the last 16 with a 4 and 3 win over Ireland's Shane Lowry.
"This is a golf course that sets up perfectly for Zach," said McIlroy.
"If he can get it in play he's going to be tough to beat. We've had some good battles over the years in the team format in Ryder Cup so tomorrow should be a good one."
Johnson's passage to the knockout rounds as Group 3 winner never looked in doubt as he raced into a commanding lead over the front nine against the Lowry.
He reached the turn at four up before a birdie on the 393-yard par four 10th took him to five up, leaving victory a formality.
Elsewhere, Australia's Jason Day became the first player to book his place in the last 16 after England's Paul Casey withdrew from their final group stage match.
Casey was forced to concede after only six holes after complaining of stomach cramps.
Casey's withdrawal ensured Day qualified as winner of Group 2 following earlier wins over Thailand's Thongchai Jaidee and Northern Ireland's Graeme McDowell.
Day will now face Brandt Snedeker, seeded 15, in Saturday's knockout round.
Bill Haas secured his passage after securing a one up victory over Australia's Adam Scott.
Haas rolled in a 12-foot birdie putt on the 18th to secure a win which saw him top Group 6 following wins over Belgium's Thomas Pieters and Chris Wood of England.
Haas however was unhappy with his long game and believes he will need to improve to advance further on Saturday.
"I struggled all day - I need to play better tomorrow if I want to advance," said Haas, who will play Chris Kirk in the next round.