Luke Donald is on course to retain his BMW PGA Championship title - and to return to world number one - after a nightmare day for overnight leader James Morrison in front of family and friends at Wentworth.
Four clear after a sparkling second round 64, the world number 236 crashed to an 81 and will go into the closing 18 holes an amazing eight strokes behind.
While local man Morrison had a quadruple bogey eight, a triple bogey eight and three bogeys on his card, Donald showed his class with a 69 - the joint best round of the day in the windy conditions.
Needing only a top eight finish to take the number one spot back off Rory McIlroy, who opened the door by missing a second successive cut, the 34-year-old is now 11 under par and two ahead of Justin Rose.
Donald is trying to follow Sir Nick Faldo and Colin Montgomerie as the only players to make a successful defence of the European Tour's flagship event.
Faldo did it in 1980 and 1981, while Montgomerie had three wins in a row from 1998 to 2000.
Former England Youth cricketer Morrison, whose only win on the circuit was in the relatively minor Madeira Islands Open in his rookie season two years ago, knew it was going to be a test for him.
"I desperately, desperately, desperately want to keep going forward," he had said. "I expect a lot, but if I shoot 80 or 65 I'll take what I can from it."
He could never have expected things to unravel as they did, however.
After a bogey on the first, where he bunkered his approach, he went out of bounds with his second on the long fourth and ran up his first eight.
That alone was enough to take him out of the lead, but the collapse continued.
He bogeyed the next and on the 391-yard eighth went from trees to water for a quadruple bogey that was matched by playing partner David Drysdale, himself twice in the lake.
The Scot had been joint leader at that point, but that was the start of a horrible slide for him too. He finished with a 78.
Donald plotted his way around like the expert he now is, gathering birdies at the first two par fives and then going two clear at the 13th.
Peter Lawrie was the man out in front with them by then, but as the Dubliner hit into the trees and bogeyed Donald fired in an iron to six feet and picked up another shot.
He did bogey the 15th after driving into a ditch, but salvaged a par on the long 17th after going in the trees and hitting an on-course television reporter with his next shot.
Then, to nobody's surprise, he laid up short of the water on the last, pitched to 18 feet and made it.
Rose, who played with Donald the first two days and admired his ability to bounce straight back from trouble, and Ian Poulter were the only others to break 70.Lawrie is in third spot on seven under after a 72, while joint fourth are former Open champion Paul Lawrie and South African trio Branden Grace, Richard Sterne and Ernie Els - the latter livid with the lack of watering on the course he re-designed.
Donald said: "The tougher the better. The good players that can be patient and deal with it are always going to rise to the top usually."
The US Open is generally regarded as the hardest of all the majors and with it coming up in just over a fortnight Donald said this week was "good prep.
"That was by far my best round of the three. The swing was swirling and I hit a lot of solid shots.
"There were a couple of loose ones coming down the stretch, but I'm very pleased with that finish - it was hugely important for me.
"Physically and mentally it was tough and it's going to be a grind tomorrow."
Rose, who could move to a career-high fifth in the world by winning, commented: "I'm delighted. It was one of those where I realise how good a round it was until I saw that the course had taken its toll.
"There were some borderline holes, as there are at US Opens and on Sundays, but I sort of relished the challenge.
"It takes all your experience and patience and it certainly tested me."
Morrison said: "With the wind and the firmness of the course it was brutal. I'm very, very disappointed but it's definitely a learning curve for me."
Collated third round scores and totals, Wentworth GC, Surrey, England
(Gbr & Irl unless stated, par 72):
205 Luke Donald 68 68 69
207 Justin Rose 67 71 69
209 Peter Lawrie 66 71 72
211 Paul Lawrie 69 71 71, Ernie Els (Rsa) 68 73 70, Branden Grace (Rsa) 69 69 73, Richard Sterne (Rsa) 71 68 72
212 Francesco Molinari (Ita) 68 70 74, Rafael Cabrera Bello (Spa) 68 70 74, Peter Hedblom (Swe) 68 70 74
213 Ian Poulter 71 73 69, James Morrison 68 64 81
214 Jeev Milkha Singh (Ind) 70 74 70, David Drysdale 66 70 78, Federico Colombo (Ita) 69 74 71, Marcel Siem (Ger) 71 67 76, David Higgins 70 70 74, Alvaro Quiros (Spa) 67 Collated third round scores & totals, Wentworth GC, Surrey, England70 77
215 Ricardo Gonzalez (Arg) 71 67 77, Pablo Martin (Spa) 69 70 76, Fredrik Andersson Hed (Swe) 70 68 77, Edoardo Molinari (Ita) 69 70 76, Simon Khan 71 74 70, Lee Westwood 70 75 70
216 Marc Warren 68 76 72, Gareth Maybin 70 70 76, Martin Kaymer (Ger) 71 69 76, Shiv Shankar Prasad Chowrasia (Ind) 69 76 71
217 Garth Mulroy (Rsa) 71 70 76, Victor Dubuisson (Fra) 70 71 76, Julien Quesne (Fra) 74 71 72, Richard S Johnson (Swe) 67 75 75, Alexander Noren (Swe) 70 74 73, Tommy Fleetwood 72 73 72, Richard Finch 76 67 74, Miguel Angel Jimenez (Spa) 71 70 76, Jamie Donaldson 67 73 77, Paul McGinley 73 71 73
218 Jose-Maria Olazabal (Spa) 70 72 76, Damien McGrane 71 72 75, Robert Rock 68 76 74, Niclas Fasth (Swe) 67 73 78, Andrew Dodt (Aus) 69 73 76, Scott Jamieson 68 75 75
219 Charl Schwartzel (Rsa) 69 71 79, Paul Streeter 71 74 74, Jbe Kruger (Rsa) 72 73 74, Danny Willett 69 71 79, Kenneth Ferrie 68 74 77
220 Matteo Manassero (Ita) 74 69 77
221 Christian Nilsson (Swe) 74 70 77, Colin Montgomerie 69 74 78, Sam Little 72 73 76, George Coetzee (Rsa) 68 77 76, Jose Manuel Lara (Spa) 72 71 78, Bradley Dredge 71 72 78, Alex Cejka (Ger) 75 70 76
222 Thomas Bjorn (Den) 74 70 78, Thongchai Jaidee (Tha) 71 72 79, Pablo Larrazabal (Spa) 70 75 77
223 Robert Jan Derksen (Ned) 71 71 81, Brett Rumford (Aus) 70 74 79, Mikko Ilonen (Fin) 74 70 79
224 Steve Webster 69 74 81, Chris Wood 73 71 80, Shane Lowry 71 74 79, Richard Green (Aus) 72 73 79, Bernd Wiesberger (Aut) 68 73 83
225 Gregory Havret (Fra) 75 67 83, Oscar Floren (Swe) 74 71 80
226 Ben Curtis (USA) 70 75 81
230 James Kingston (Rsa) 71 74 85
