(CNN) -- Rory McIlroy battled back from a poor start to claim his second straight major title in the fading gloom of Valhalla Sunday with a one-shot victory over Phil Mickelson in the PGA Championship.
In near pitch darkness, the 25-year old from Northern Ireland parred the final hole for a three-under 68 to finish on 16-under 268 and deny American veteran Mickelson his sixth major title at 44 years of age.
McIlroy was winning the Wanamaker Trophy for the second time and his fourth major, consolidating his status as world number one.
The overnight leader trailed Rickie Fowler by three shots as he turned for his back nine but rekindled his hopes with a stunning eagle on the par-five 10th to go 14-under.
But up ahead, Fowler was joined on 15-under by playing partner Mickelson and Sweden's Henrik Stenson, who was also making a tremendous last round charge.
McIlroy, bidding for his third straight victory after his British Open and WGC-Bridgestone titles, refused to be daunted and a birdie on the 13th saw him draw level.
First Stenson, then Fowler and Mickelson dropped shots to go back to 14-under and when McIlroy birdied the 17th he led by two playing the last.
With the light fading fast, Fowler and Mickelson agreed to let McIlroy and his last day partner Bernd Wiesberger of Austria to also hit their tee shots on the 18th, effectively playing it as a fourball.
McIlroy nearly found the water with his drive and had to settle for his par, while Mickelson made his birdie to edge ahead of Fowler and Stenson into second place.
American pair Jim Furyk and Ryan Palmer finished on 12-under in joint fifth.
McIlroy thanked Mickelson and Fowler for their sportsmanship as he accepted the trophy and said there was never any doubt in his mind he would finish the job Sunday.
"I wanted to win this thing and get out of here," he said.
His latest triumph completed a remarkable run for McIlroy, who had endured a difficult 2013 after first PGA Championship success two years ago.
"I'd never dreamed I'd have a summer like this," he admitted.
Only the U.S. Masters title now eludes McIlroy to complete a full set of the majors and he will surely focus his efforts on the 2015 edition at Augusta in search of a hat-trick of successes at golf's highest level.