Rory McIlroy of Northern Ireland kisses the Wanamaker Trophy after winning the 2014 PGA Championship at Valhalla Golf Club in Louisville, Kentucky, Aug 10, 2014. [Photo/Agencies]

LOUISVILLE, Ky. - The challenge finally arrived for Rory McIlroy, and he was better than ever Sunday to win the PGA Championship.

On a back nine filled with clutch shots and as much tension as a major can provide, McIlroy emerged from a four-man race to outlast Phil Mickelson and the darkness at Valhalla to capture his second straight major.

McIlroy closed with a 3-under 68 and became only the fourth player in the last century of golf to win four majors at 25 or younger. The others were Tiger Woods, Jack Nicklaus and Bobby Jones, three of the game's greatest players.

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"I didn't think in my wildest dreams I'd have a summer like this," said McIlroy, only the seventh player to win the last two majors of the year. "I played the best golf of my life. I really gutted it out today."

But one of the greatest shows on soggy turf came with a most peculiar ending.

Three shots behind going to the back nine, McIlroy rallied to take the lead and then hit a 9-iron from the fairway bunker to 10 feet for birdie on the 17th hole for a two-shot lead going to the par-5 18th. Because of a two-hour rain delay earlier, darkness was falling quickly and it wasn't certain McIlroy would be able to finish.

McIlroy was allowed to hit his tee shot before Mickelson and Rickie Fowler had reached their drives. Both were only two shots behind, still in the game. McIlroy came within a yard of hitting in a hazard right of the fairway.

Then, the PGA of America allowed McIlroy to hit his second shot. Mickelson and Fowler had to stand to the side of the green.

"We were cool with hitting the tee shot," Fowler said. "We weren't expecting the approach shots."

Fowler had a 50-foot eagle attempt to tie for the lead. He was well off the mark, and missed the short birdie putt attempt that cost him his third straight runner-up finish in a major. Mickelson was short of the green, and his chip came within inches of dropping for an eagle that would have tied him for the lead.

Mickelson appeared upset that they had to wait to finish the hole _ not standard procedure in a PGA Tour event _ and he made two references in a TV interview that this is the only championship the PGA of America runs all year.

"It didn't affect the outcome of the championship at all, I don't think," Mickelson said. "It's not what we normally do. It's not a big deal either way."

Mickelson closed with a 66 and was runner-up for the ninth time in a major.