World number one Rory McIlroy edged a gripping US PGA Championship in near darkness at Valhalla to become the first UK player to win back-to-back majors.

Three players were still in contention at the final hole, with heavy rain having earlier led to a two-hour delay.

A see-saw battle on the back nine witnessed four different players sharing the lead at some stage.

But it was the Northern Irishman who dug deep to follow his Open success.

The 25-year-old had earlier seen his overnight one-shot lead wiped out on the front nine and was three shots behind the leaders at one point before taking control after the turn.

A three-under 68 on the final day saw off Phil Mickelson, with Rickie Fowler and Henrik Stenson a shot further adrift.

Rory later credited the “best golf of his life” with producing a summer beyond his “wildest dreams”.

However McIlroy would not have finished the day were it not for a fine display of sportsmanship from Mickelson and Fowler. The pair were in the group ahead and allowed him to play up behind them as he tried to beat the fading light following the rain delay, then waited on the side of the 18th green to applaud the new champion.

Flashlights illuminated the night sky as McIlroy showed sheer relief after holing out his final putt, fist-pumping the air and celebrating on the course with his father Gerry before receiving the huge Wanamaker Trophy.

McIlroy’s resurgence on the back nine capped an enthralling final day and saw him become the third youngest player of the modern era – after Tiger Woods and Jack Nicklaus – to win four of golf’s biggest prizes, while he also becomes the first man to win back-to-back majors since Ireland’s Padraig Harrington in 2008.

Heavy downpours threatened to take the championship into a fifth day

An ever-changing leaderboard saw an early five-way tie – between Fowler, Mickelson, McIlroy, Stenson and Bernd Wiesberger – transform into a narrow advantage for 25-year-old Fowler around the turn.

The competition then became a see-saw battle with Fowler, playing partner Mickelson, Stenson and McIlroy all taking a share of the lead over the back half.

But McIlroy rediscovered the mental resilience shown in his recent win at Hoylake to emerge as a worthy winner.

Having fallen three shots behind Fowler after six holes, he swung the momentum back in his favour with a majestic eagle three at the 590-yard 10th.