Pre-tournament favourite Rory McIlroy recovered from a stumbling start to overcome a series of challengers and clinch his fourth major title by a shot at the PGA Championship.
Final leaderboard (top-6)
268 Rory McIlroy
269 Phil Mickelson
270 Rickie Fowler
272 Jim Furyk
A stroke in front of the chasing pack overnight, the Northern Irish world number one lost the lead but regained control after the turn, signing off with a three-under-par 68 at Valhalla Golf Club for a 16-under total of 268.
Phil Mickelson, the 2005 winner, birdied 18 to finish alone in second with a closing 66, with Swede Henrik Stenson (66) and American Rickie Fowler (68) a stroke further back in third.
"I didn't think in my wildest dreams I'd have a summer like this," British Open champion McIlroy told CBS Sports after being presented with the coveted Wanamaker Trophy.
"I've just played the best golf of my life and just really gutted it out today. It was a little different from the previous major wins that I've had and I think I showed a lot of guts out there today to get this job done."
In gathering gloom at Valhalla, where play was suspended for just under two hours earlier in the day due to water-logged conditions, McIlroy parred the last to win his third consecutive title on the PGA Tour, and his second major this year.
The 25-year-old, who won the 2012 PGA Championship at Kiawah by a record eight shots, became the fourth youngest player to land four majors, with only Tom Morris Jr, Jack Nicklaus and Tiger Woods ahead of him.