Jordan Spieth comfortably outplayed Rory McIlroy in their keenly anticipated Masters showdown Saturday, but found himself under threat instead from an unlikely trio of pursuants after a dismal last hole.
The 22-year-old defending champion led the tournament by one from the 26-year-old from Northern Ireland at the start of the day.
But their head-to-head duel never really materialized and, by the end of it, Spieth was five clear of his rival as McIlroy's hopes of a career Grand Slam were severely compromised.
The American, seeking to become just the fourth player to win back-to-back Masters, fired at 73 to finish the day on three-under par 213, leading the tournament for a record seventh straight time, four coming last year when he won his first major.
Despite an erratic display off the tee, he walked away with a one-stroke lead over American debutant Smylie Kaufman, with Asia's top player, Hideki Matsuyama, and German veteran Bernhard Langer a stroke further back.
It could have been even better for Spieth, but he made a mess of the 18th and took a double bogey.
"I am in the position I wanted to be in after 54 holes and think about it that way and not about the way I finished today," he said.
"I played better than I scored. It was a tough position to have a four-shot lead and to now it's being anyone's game. It's hard to swallow and it's mixed feelings right now."
The leading quartet were the only players from among the 57 who made the cut to end the day under par overall as Augusta National bared its teeth through gusting winds and super-slick greens that left many in despair.
On level par were world number one Jason Day, American Dustin Johnson and England's Danny Willett.
While Spieth held onto his lead as he seeks to become just the fourth player to win back-to-back Masters titles -- after Tiger Woods, Nick Faldo and Jack Nicklaus -- it was the evergreen Langer who stole the show.
The 58-year-old, two-time former winner, playing in his 33rd Masters, started the day five adrift of the American, 36-years his junior.
But in a remarkable display of shotmaking and pinpoint putting in the toughest of conditions, Langer held firm and then knocked in three straight birdies from the 13th to move into contention.
A double-bogey six at the last took some of the shine away from his performance, but he remained in with a chance of becoming by a long way the oldest-ever winner of a major title.
He would be 10 years older than Julius Boros, who was 48 when he won the 1968 PGA Championship.
Experience of playing over Augusta National counted for much, the German said.
"There's different ways of getting there, and obviously it's a lot easier for these young guys, hitting a lot less club into some of the greens," he said.
"But when I play really, really good, when I bring my A-game, I can still compete, and even on a very long golf course like this."
The 24-year-old Kaufman, who was playing in the developmental Web.Com tour last year, came in with a 69, the only sub-70 round since Thursday.
Playing in just his second major tournament after the 2014 US Open when he missed the cut, Kaufman admitted that he is still staying with his parents back home in Alabama.
Against all odds, he will now play with close friend Spieth in the final pairing of the Masters on Sunday afternoon.
Explaining his mindset for that he said: "You know, I'm going to hang out with my buddies and friends and family, do the same things we've been doing all week, just hang out and try to keep it pretty casual and hopefully I sleep good."
Matsuyama was the first Japanese player to finish top amateur in the Masters in 2009 and he is aiming to become just the second Asian man to win a major after Yang Yong-Eun of South Korea in the 2009 PGA Championship.
He came close to dislodging Spieth from the top position, getting to within one shot of him down the back nine, but bogeys at 16 and 17 pulled him back.
