WENTWORTH, United Kingdom, May 26, 2012 (AFP) - Morrison had been four shots clear after a second round 64, but the world number 236 carded a woeful 81 on Saturday to leave him eight strokes behind Donald heading into Sunday's final round.
As England's Morrison struggled to recover after a quadruple bogey eight, a triple bogey eight and three other bogeys, Donald made light of testing conditions to take the lead.
His 69 was the joint best round of a windy day and the Englishman is well on course to secure the top eight finish needed to seize the number one spot from Rory McIlroy, who missed a second successive cut on Friday.
The 34-year-old is now 11 under par and two shots ahead of second placed Justin Rose as he bids to follow Nick Faldo and Colin Montgomerie as the only players to make a successful defence of the European Tour's flagship event.
"That was by far my best round of the three. The swing was swirling and I hit a lot of solid shots," Donald said.
"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."
A defiant Morrison added: "I desperately, desperately want to keep going forward. I expect a lot, but if I shoot 80 or 65 I'll take what I can from it."
Rose, who could move to a career-high fifth in the world by winning on Sunday, was one of only three players to break 70 in testing conditions.
"I'm delighted," he said. "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."
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, who was furious with tournament organisers for not keeping the greens well watered.
"I asked them to put water on the greens, so put f***ing water on the greens," Els said.
"You don't have to be a rocket scientist to figure it out. The guys are not happy and I'm with them. The Tour has got to play ball, it's not my job."
Lee Westwood was unable to close the gap on the leaders as the Englishman's hopes of ending his long wait for victory at Wentworth were shattered.
Westwood is making his 19th appearance here and came in with high hopes of lifting the trophy after losing a play-off to Donald last year.
But the 39-year-old's erratic form this week, 18 birdies in three days have been offset by eight bogeys, three doubles and a triple, has left him well off the pace.
"I've just got a destructive one in there. It's a bit of a pull hook and it's my bad shot when I'm not swinging well," Westwood said.
"I'm a bit tired. I've played a lot this year already."
Leading scores after the third round of the European Tour PGA Championship at Wentworth on Saturday (par 72):
205 - Luke Donald (ENG) 68 68 69
207 - Justin Rose (ENG) 67 71 69
209 - Peter Lawrie (IRL) 66 71 72
211 - Paul Lawrie (SCO) 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 (ESP) 68 70 74, Peter Hedblom (SWE) 68 70 74
213 - Ian Poulter (ENG) 71 73 69, James Morrison (ENG) 68 64 81
214 - Jeev Milkha Singh (IND) 70 74 70, David Drysdale 66 70 78 (SCO), Federico Colombo (ITA) 69 74 71, Marcel Siem (GER) 71 67 76, David Higgins 70 70 74, Alvaro Quiros (ESP) 67 70 77
215 - Ricardo Gonzalez (ARG) 71 67 77, Pablo Martin (ESP) 69 70 76, Fredrik Andersson Hed (SWE) 70 68 77, Edoardo Molinari (ITA) 69 70 76, Simon Khan 71 74 70 (ENG), Lee Westwood (ENG) 70 75 70
216 - Marc Warren (SCO) 68 76 72, Gareth Maybin (NIR) 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 (ENG) 72 73 72, Richard Finch (ENG) 76 67 74, Miguel Angel Jimenez (ESP) 71 70 76, Jamie Donaldson (WAL) 67 73 77, Paul McGinley (IRL) 73 71 73
218 - Jose-Maria Olazabal (ESP) 70 72 76, Damien McGrane (IRL) 71 72 75, Robert Rock (ENG) 68 76 74, Niclas Fasth (SWE) 67 73 78, Andrew Dodt (AUS) 69 73 76, Scott Jamieson (SCO) 68 75 75
219 - Charl Schwartzel (RSA) 69 71 79, Paul Streeter (ENG) 71 74 74, Jbe Kruger (RSA) 72 73 74, Danny Willett (ENG) 69 71 79, Kenneth Ferrie (ENG) 68 74 77
220 - Matteo Manassero (ITA) 74 69 77
221 - Christian Nilsson (SWE) 74 70 77, Colin Montgomerie (SCO) 69 74 78, Sam Little (ENG) 72 73 76, George Coetzee (RSA) 68 77 76, Jose Manuel Lara (ESP) 72 71 78, Bradley Dredge (WAL) 71 72 78, Alex Cejka (GER) 75 70 76
222 - Thomas Bjorn (DEN) 74 70 78, Thongchai Jaidee (THA) 71 72 79, Pablo Larrazabal (ESP) 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 (ENG) 69 74 81, Chris Wood (ENG) 73 71 80, Shane Lowry (IRL) 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