Rory McIlroy won his second major with a dominant display in the US PGA Championship, finishing eight stokes clear of his nearest rival.

The 23-year-old shot a six-under 66 to finish the tournament on 13 under par, well clear of the relatively unknown Englishman David Lynn who finished on five under after an impressive final round of 68.

At one point it had looked as though McIlroy's nearest rival would be his Ryder Cup colleague Ian Poulter, who began the final round in impressive fashion as he secured six birdies in the first seven holes.

Rory McIlroy
Rory McIlroy wins his second major with a dominant display at the USPGA [Reuters]

However, his challenge faded on the back nine as three successive bogeys left him well off the pace, while Sweden's Carl Petterson saw his challenge collapse on the opening hole, as he accrued a two-shot penalty for allowing his clubhead to touch the ground before striking the ball.

The Swede still impressed as he holed four birdies to finish four under, and secure his best finish at a major.

Other challengers fell by the wayside as Tiger Woods failed to ever get going in his final round, and it became a procession for McIlroy who became the youngest-ever winner of the USPGA and secured his return to the top of the world rankings.

"I don't think I have let it sink in yet - it was a great round of golf - I am speechless," said McIlroy. "I got off to a bit of a shaky start, but settled into it and I thought my putting today was phenomenal.

"Thanks dad and thanks mum - I'm sure she's watching at home. I had a good feeling at the start, but I never imagined doing this" McIlroy said.

"It means an awful lot to look at the names on that trophy and put mine alongside them."

The major was also the last opportunity for America's golfers to seal their place in the Ryder Cup team, and a poor final round from Bo van Pelt meant that he missed automatic qualification as Phil Mickelson was assured eighth place.

Mickelson will be joined by Woods, Bubba Watson, Jason Dufner, Keegan Bradley, Webb Simpson, Zach Johnson and Matt Kuchar, while captain Davis Love III will name his four captain's picks on 4 September.