LOUISVILLE, Kentucky (AP) ― The challenge finally arrived for Rory McIlroy, and he was better than ever to win the PGA Championship.

On a back nine filled with as much tension as a major can provide, McIlroy emerged from a four-man battle with flawless golf to outlast Phil Mickelson and the darkness Sunday at Valhalla and 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.

McIlroy hit a 9-iron from a fairway bunker on the 17th hole to 10 feet and made the birdie putt to take a two-shot lead to the par-5 18th. Because of a two-hour rain delay, darkness was falling quickly and it wasn’t certain McIlroy would be able to finish.

He was allowed to tee off even before Mickelson and Rickie Fowler had reached their golf balls in the fairway. Both were only two shots behind and still in the game. McIlroy came within a yard of hitting into a hazard right of the fairway. Mickelson and Fowler had to stand to the side of the green to allow McIlroy to play his second shot.

The 25-year-old from Northern Ireland hit into a bunker and had to two-putt from 35 feet for a one-shot win.

Moments earlier, Mickelson came within inches of chipping in for eagle. He settled for a 6-under 66 and a runner-up for the ninth time in a major. Fowler, the first player in history to finish in the top five at all four majors without winning, also had a chance with a long eagle putt. He missed badly, and then missed the short birdie putt.

Fowler closed with a 68 and tied for third with Henrik Stenson, who also had a share of the lead until missing a 3-foot par putt on the 14th putt.