Jason Day threw away his chance of a second US PGA title with "one crazy decision" according to six-time major winner Nick Faldo.
Day was four shots off the lead playing the final hole at Quail Hollow when he attempted a highly risky recovery shot around a tree just two yards in front of him.
The former world number one succeeded only in sending his ball into some bushes, from where he had to take a penalty drop and pitch over more shrubbery into the rough to the right of the fairway.
From there Day came up short of the green and three-putted to card a quadruple-bogey eight, dropping him back to level par and seven behind playing partner Kevin Kisner, who had double-bogeyed the 16th and bogeyed the last.
Commentating for CBS, Faldo said: "That's one of the craziest decisions I have ever seen a professional make, that second shot.
"I can't believe Col Swatton (his caddie) did not give him a wedge and start walking, say that's the only choice mate.
"That is his PGA right out of the window with one crazy decision."
The late drama came after a largely uneventful day and left Kisner with a one-shot lead over Japan's Hideki Matsuyama and compatriot Chris Stroud, who secured the final place in the field by winning his first PGA Tour title at the 289th time on Sunday.
Matsuyama, who won the WGC-Bridgestone Invitational last week, could only add a 73 to his course-record 64 on Friday, with Justin Thomas and Louis Oosthuizen a shot further back on five under.
Kisner looked to be in command of the tournament after taking a two-shot lead with birdies on the 14th and 15th, only to pull his second shot to the 16th into the water.
The South Carolina native then saw his approach to the 18th bounce off a bridge spanning the creek which runs the length of the hole, but he was able to salvage a bogey from a difficult lie in the thick rough.
"I'm happy I'm in the position I'm in," Kisner said after a round of 72. "I had a chance to run away from guys and take people out of the tournament that were four or five, six back, and I didn't do it.
"Now I'm in a dogfight tomorrow and I have to be prepared for that.
"I've seen my game trending, even though I haven't played great the last month and a half. But I've been working hard and seeing a lot of good things and I know the golf course.
"I think that's really beneficial for me here, unlike other majors that we play once every five years or something."
Oosthuizen's bid for a second major title looked in jeopardy after he injured himself pulling off a miraculous escape shot from the base of a tree on the second.
The impact jarred his forearm and bent his eight iron out of shape - it was later repaired and returned to him on the 11th - but the 2010 Open champion still produced a slinging hook to find the green and save par.
"I looked up just before I hit it and I told my caddie, 'I'll show you a little trick shot here,'" the South African explained.
"I saw something in front of the ball but I didn't think it was a root - I thought it was something loose. I banged the eight iron against it pretty bad and immediately my forearm got a shock.
"Then in the next five minutes it started to cramp up and it got really tight. Luckily on six we had a bit of a wait and my physio could release it a bit.
"I felt it a little bit on the 14th tee again on a different spot but I was never hurt so it was fine. I was just scared it was going to tighten up really badly but it should be fine."
Seventeen players are within seven shots of the lead heading into the final round, but Rory McIlroy already had one eye on next season after a third year without a major title was effectively confirmed.
McIlroy came into the week as the pre-tournament favourite on the back of top-five finishes in his last two starts and a brilliant record at Quail Hollow, including two wins and a course record of 61 in 2015.
However, changes to several holes and a switch to bermuda rough and greens have not suited the world number four, whose last major title came in the 2014 US PGA at Valhalla.
A third round of 73 left McIlroy four over par and a shot behind Open champion Jordan Spieth, as well as 11 behind Kisner.
Asked how far away he was from his best after a year which has included injury, a change of equipment, his wedding and a split from long-term caddie JP Fitzgerald, McIlroy simply replied: ''Looking forward to 2018.''
After a week off, McIlroy plans to play in all four FedEx Cup play-off events as he attempts to retain the title - and 10million US dollar bonus - he won last year.