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 and local boy 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 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 - and is now 11 under par and two ahead of Justin Rose.
Donald needs 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, but he is also 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.
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, bogeyed the first, where he bunkered his approach, then 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 partner David Drysdale, himself twice in the lake. The Scot was then joint leader, but that was the start of a horrible slide for him too and 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. Lawrie ended day three in third spot on seven under after a 72, while joint fourth are Scot Paul Lawrie and South African trio Branden Grace, Richard Sterne and Ernie Els.
Donald 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.