KIAWAH ISLAND, South Carolina, Aug 12, 2012 (AFP) - The 23-year-old Northern Irishman surpassed Luke Donald to become the No. 1 ranked player in the world as he closed with a six-under 66 in the final major championship of the season.
McIlroy capped his brilliant bogey-free performance with a 24-foot birdie putt on the last hole to reach a 13-under 275 total. 
The challengers all fell by the wayside as McIlroy earned his second dominating major championship win. He won the 2011 US Open also by a whopping eight strokes.
England's David Lynn finished alone in second after shooting a four-under 68 to finish at five-under 283. Justin Rose (66), Ian Poulter (69), Keegan Bradley (68) and McIlroy's playing partner Carl Pettersson (72) finished in a four-way tie for third at four-under 284.
Blake Adams, Jamie Donaldson, Peter Hanson and Steve Stricker all finished at three under, 10 shots adrift of McIlroy.
McIlroy, who earned $1.4 million in prize money, ended up having to play 27 holes on Sunday. He began his fourth round with a three-stroke lead after finishing off nine holes of the suspended third round early Sunday.
More than three inches (seven centimeters) of rain have fallen on the Kiawah Island Golf Resort course this week resulting in some of the most difficult playing conditions ever for a PGA Championship and creating problems with the scheduling.
McIlroy became the first player this year to convert a 54-hole lead in a major championship into a victory.
He got off to a solid start by making birdie on two of his first three holes in the final round. While his start was superb, he saved his best for the last as he drained a 24-foot putt on 18 to put an emphatic stamp on the win.
Lynn made the most of his PGA Championship debut as he posted three birdies, including two straight, on the more difficult back nine.
Pettersson, Poulter, Rose and Tiger Woods all threatened at certain times of the weekend but no one was able to keep pace with the on-fire McIlroy down the stretch.
Woods, who was chasing his 15th career major title, shot a final round even-par 72 to finish in a tie for 11th at two-under 288.
He could have surpassed Donald for the world number one ranking this week with a win but the top spot ended up going to McIlroy after Donald finished well back in a tie for 32nd.
Poulter got off to a flying start in the fourth round, rolling in five birdies in a row, including a 20-footer at the fifth to get within one shot of McIlroy. But he couldn't maintain it on the back nine and slipped down the leaderboard.
Final scores on Sunday in the fourth round of the PGA Championship at par-72 Kiawah Island Resort (Ocean Course), Kiawah Island, South Carolina (USA unless stated):
275 - Rory McIlroy (NIR) 67 75 67 66
283 - David Lynn (ENG) 73 74 68 68
284 - Justin Rose (ENG) 69 79 70 66, Keegan Bradley 68 77 71 68, Ian Poulter (ENG) 70 71 74 69, Carl Pettersson (SWE) 66 74 72 72
285 - Blake Adams 71 72 75 67, Jamie Donaldson (WAL) 69 73 73 72, Peter Hanson (SWE) 69 75 70 71, Steve Stricker 74 73 67 71
286 - Ben Curtis 69 77 73 67, Bubba Watson 73 75 70 68, Tim Clark (RSA) 71 73 73 69, Geoff Ogilvy (AUS) 68 78 70 70, Graeme McDowell (NIR) 68 76 71 71, Tiger Woods 69 71 74 72, Adam Scott (AUS) 68 75 70 73
287 - John Daly 68 77 73 69, Padraig Harrington (IRL) 70 76 69 72, Bo Van Pelt 73 73 67 74
288 - Joost Luiten (NED) 68 76 74 69, Louis Oosthuizen (RSA) 70 79 70 69, Robert Garrigus 74 73 74 67, Pat Perez 69 76 71 72, Seung-yul Noh (KOR) 74 75 74 65, Jimmy Walker 73 75 67 73
289 - Thorbjorn Olesen (DEN) 75 74 71 69, Miguel Angel Jimenez (ESP) 69 77 73 71, Jason Dufner 74 76 68 71, Marc Leishman (AUS) 74 72 71 72, Trevor Immelman (RSA) 71 72 70 76
290 - John Senden (AUS) 73 74 72 71, Greg Chalmers (AUS) 70 76 72 72, Bill Haas 75 73 69 73, Luke Donald (ENG) 74 76 74 66
291 - Fredrik Jacobson (SWE) 71 75 73 72, Rich Beem 72 76 72 71, Phil Mickelson 73 71 73 74, Y.E. Yang (KOR) 73 74 74 70, Marcel Siem (GER) 72 73 71 75, Vijay Singh (FIJ) 71 69 74 77
292 - J J Henry 72 77 70 73, Jim Furyk 72 77 70 73, Aaron Baddeley (AUS) 68 75 74 75, Gary Woodland 67 79 75 71, David Toms 72 78 72 70, Martin Laird (SCO) 71 74 79 68
293 - Paul Lawrie (SCO) 73 75 71 74, Ernie Els (RSA) 72 75 73 73, Dustin Johnson 71 79 72 71, Thomas Bjorn (DEN) 70 79 74 70, Retief Goosen (RSA) 73 75 75 70, Scott Piercy 68 78 78 69
294 - Francesco Molinari (ITA) 70 75 74 75, Sang-moon Bae (KOR) 72 78 71 73, Darren Clarke (NIR) 73 76 72 73, Brendon De Jonge (ZIM) 71 78 72 73, K J Choi (KOR) 69 77 75 73
295 - Charl Schwartzel (RSA) 70 77 74 74, Ryo Ishikawa (JPN) 69 77 79 74, 296 - K.T. Kim (KOR) 69 77 77 73
297 - Gonzalo Fernandez-Castano (ESP) 67 78 75 77, Chez Reavie 74 76 73 74, Ken Duke 71 78 74 74, George McNeill 71 76 80 70
298 - Alexander Noren (SWE) 67 80 73 78, Marcus Fraser (AUS) 74 75 78 71
299 - Toru Taniguchi (JPN) 72 76 78 73, John Huh (KOR) 72 78 79 70
300 - Zach Johnson 72 73 76 79
304 - Matthew Every 72 76 74 82
306 - Cameron Tringale 69 78 77 82