Rory McIlroy
Rory McIlroy poses with the Wanamaker Trophy after winning the 2014 PGA Championship in Louisville.Reuters

Rory McIlroy became the first golfer to win back-to-back major titles after Padraig Harrington in 2008, as he held off Phil Mickelson's charge on a rain-soaked Valhalla Golf Club on Sunday.

McIlroy went into the fourth round with a one-stroke advantage, which he soon lost after bogeying on the third and sixth holes. The Irishman, after initial hiccups, made a dramatic turnaround to win his second major title inside three weeks.

The world number one won the British Open at the Royal Liverpool Golf Club in emphatic fashion, and although he wasn't as dominant in Louisville, he confirmed his place as the world's best current golfer.

"It is the most satisfying," McIlroy said. "To win it in this fashion and this style, it means a lot. It means that I know that I can do it. I know that I can come from behind. I know that I can mix it up with the best players in the world down the stretch in a major and come out on top."

McIlroy completed a hat-trick of victories and is on the longest winning streak since Tiger Woods' five tournament wins in 2008. The 25-year-old finished the Championship 16-under par 268, while Mickelson was just one shot adrift, followed by Henrik Stenson and Rickie Fowler on tied third.

The Irishman struck two bogeys in the third and sixth, which was followed by a birdie. On the other hand, Mickelson displayed a much better performance and played consistently during the whole afternoon.

The American got the better of everyone on the course with his ever-improving game, except McIlroy, who lifted his game when it mattered most, and struck an eagle on the 10th. Mickelson replied with a birdie in the following hole but a bogey in the 15th virtually ended his title hopes.

"Regardless of how I played this week, I know that I've got to address some things these next three or four months," Mickelson said. "And I think that the next four or five years, I really want to make special, and then we'll see.

"I feel like I'm a lot closer to great play than what this year showed, and this is just a little glimpse of what I feel I can do and I'll see if I can work on it some. I'm optimistic that I'll be able to address these issues."

Meanwhile, Fowler, who played a consistent third round, hitting four birdies, was not at his best in the final round. He made a terrible start, as he bogeyed on the fifth, which was followed by three consecutive birdies before another bogey on 14th saw his final round flounder.

"This is probably the one that hurts the most for me with the majors this year," Fowler said. "I just wish I could have given myself a couple of better looks on the last couple holes."

Watch the highlights of the US PGA Championship HERE, HERE and HERE.