Rory McIlroy slumped out of the WGC-Accenture Match Play Championship after being taken to a 19th hole by American Harris English.
World number seven McIlroy appeared to have victory in his second-round match at Dove Mountain within his grasp as he hit form on the back nine.
The Northern Irishman won four out of five holes to lead by one after 16 but English, impressive winner over Lee Westwood in round one, replied to take the contest to sudden death.
It was at the first extra hole that McIlroy's touch deserted him as he failed to recover from a poor tee shot.
He went wide to the left and could then only pitch into desert rough between a bush and a tree. From there he overshot the green and there was no way back.
It was a disappointing end to a high-quality contest in which few other holes had been settled by mistakes.
English twice led on the front nine but his successes on the second and seventh were immediately cancelled out by McIlroy and the match was all square again at the turn.
McIlroy might have rued a missed putt at the ninth that would have put him ahead when English struck out by taking the 10th and 11th.
But McIlroy, whose iron play had been outstanding, found his touch on the greens to win the 12th, 14th, 15th and 16th, all with birdies, and edge ahead for the first time.
But English stemmed that momentum with a birdie of his own at 17 and he held his nerve to prevail on the 19th.
English said: "I had to bring my 'A' game to beat him. Rory really fought back hard, birdying 14 through 16. I knew I needed to make something happen on 17 and 18."
McIlroy's fellow Ulsterman Graeme McDowell had better fortune as he produced a stirring comeback for a second day in succession to beat Hideki Matsuyama on the 18th.
McDowell was four down after seven holes of his first round against Gary Woodland and a similar scenario unfolded as Matsuyama won three of their first six.
Yet McDowell had not been playing badly and he was certainly out of luck as Matsuyama chipped in from the rough at the second.
The 2010 US Open winner maintained a steady course and birdies at the eighth and ninth set up a tight back nine.
Matsuyama eventually cracked when he missed a short putt at the 17th to allow McDowell back level and the Japanese player compounded that error by putting his tee shot at the last into a bunker.
McDowell parred the hole to complete another fine fightback and will now face Hunter Mahan in a repeat of the decisive match at the 2010 Ryder Cup.
The 34-year-old admitted he was drained after two high-intensity victories.
McDowell said: "After the round yesterday I was pretty beat and I expect to hit the wall in about half an hour.
"That adrenaline surge in the last few holes is a bit like a Sunday afternoon.
"I was hoping to not expend as much emotion but that didn't happen.
"It was another emotional day, but I guess I am just happy to still be standing."
Top seed Henrik Stenson advanced no further as he was beaten 4&3 by Louis Oosthuizen.
Defending champion Matt Kuchar came from one down with six to play to beat Ryan Moore one up.
Sergio Garcia overcame Bill Haas 3&1 after winning four out of six holes in a strong sequence on the back nine.
The Spaniard will next play Rickie Fowler, who won a high-quality match with this season's form player Jimmy Walker one up.
French Ryder Cup hopeful Victor Dubuisson saw an early three-hole lead wiped out, but recovered his poise to beat Peter Hanson 3&1.
Bubba Watson, who led by three after just four holes, survived a late wobble before seeing off Jonas Blixt two up.
Blixt threatened to make life difficult by winning the 12th and 14th, but short missed putts at the 15th and 16th and a penalty drop on the last ended his hopes.
American youngster Jordan Spieth produced one of the day's most impressive performances, beating Thomas Bjorn 5&4.