San Francisco - World number one Rory McIlroy and England's Paul Casey battled to a standstill in the $9.25 million WGC-Championship Match Play in California on Saturday and face a dawn start to resume their match for a place in the last four.
In near-darkness at Harding Park, the two European stars finished all square after 21 holes and will continue their sudden death battle on Sunday morning at 06:45.
McIlroy missed a six foot birdie putt to snatch victory on the third sudden death hole leaving Casey relieved to have survived.
"I dodged a couple of bullets but I gave him a couple too," Casey said. "I'm glad we're coming back tomorrow, I thought that was it for the day and the week," he added referring to McIlroy's missed putt.
McIlroy was left ruing his inability to close out the win.
"It was good, it was back and forth," he said. "I had a couple of opportunities to close it out but I couldn't quite convert.
"It was getting pretty dark so we'll come back in the morning and try again."
McIlroy, superb in a 6&5 thrashing of Hideki Matsuyama in the last 16, started his quarter-final as he had finished the previous round, claiming a birdie on the first to go one up.
But Casey hit back with three birdies of his own on the front nine to go two up at the turn.
McIlroy slowly hauled himself back into contention, draining a 20-foot birdie putt on the 10th to reduce Casey's lead.
A bogey by Casey on the par-three 13th put the match all square but then McIlroy's first bogey of the day handed the initiative back to his opponent on 14.
After halving the par-four 15th, McIlroy looked to be poised to cancel out Casey's lead as he prepared for a five-foot birdie putt.
Casey however coolly rolled in a difficult putt for birdie from just off the green to cling on to his lead with two holes left.
But the Englishman's luck ran out on the 17th as McIlroy punished a jittery putting display by his opponent.
McIlroy chipped from heavy rough to five feet to put the pressure on Casey, who then over hit a long putt from the collar several feet past the hole before two putting.
Both players found the rough off the tee on the par-five 18th, and McIlroy was unable to find the green with his second which landed just shy of a bunker.
Casey's 16-foot birdie putt rolled up just shy of the cup leaving McIlroy a 12-footer for victory.
McIlroy's effort also missed, however, taking the match to the sudden death stalemate.
The winner of the quarter-final will face fifth-ranked Jim Furyk in the semi-finals. Furyk produced a sparkling performance on the back nine to defeat Louis Oosthuizen of South Africa 4&2.
Oosthuizen had led by one hole at the turn, but four birdies in the next seven holes by Furyk saw him wrap up a comfortable win.
In Sunday's other semi-final, England's Danny Willett, ranked 49, will face Gary Woodland of the United States, the world number 52.
Willett upset English veteran Lee Westwood in the last 16 before going on to down compatriot Tommy Fleetwood in another all-English duel in the quarter-finals.
Willett advanced to the last four after shooting four birdies and two bogeys to win 4&3.
Scores at San Francisco's Harding Park golf course on Saturday in the
$9.25 million WGC-Championship Match Play (x denotes ranking):
Rory McIlroy (NIR x1) vs Paul Casey (ENG). All square after 21 holes; play to resume Sunday.
Gary Woodland (USA x52) bt John Senden (AUS x65) 5&3
Danny Willett (ENG x49) bt Tommy Fleetwood (ENG x57)
Jim Furyk (USA x5) bt Louis Oosthuizen (RSA x30) 4&2
Round of 16
Gary Woodland (USA x52) bt Marc Leishman (AUS x60) 2&1
John Senden (AUS x65) bt Hunter Mahan (USA x32) 2&1
Tommy Fleetwood (ENG x57) bt Branden Grace (RSA x39) 2&1
Danny Willett (ENG x49) bt Lee Westwood (ENG x27) 3&2
Jim Furyk (USA x5) bt JB Holmes (USA x12) 5&3
Rory McIlroy (NIR x1) bt Hideki Matsuyama (JPN x16) 6&5
Louis Oosthuizen (RSA x30) bt Rickie Fowler (USA x13) 1-up
Paul Casey (ENG x37) bt Charl Schwartzel (RSA x38) 3&1