Race to Dubai winner Henrik Stenson and American Rickie Fowler hit the front as Rory McIlroy found himself with a real fight on his hands to win his second major in four weeks as the weather-affected US PGA Championship headed towards a thrilling climax at Valhalla.
With the course already saturated, a torrential downpour saw play suspended at 12:53pm local time, more than two hours before the final pair had been scheduled to tee off.
Play was eventually able to resume at 2:44pm with McIlroy and Austria's Bernd Wiesberger starting at 4:19pm, meaning they faced a race against time to finish before darkness descended in Louisville.
"I will hang around until next week to try to win this thing. It doesn't bother me in the slightest," McIlroy insisted before discovering he also faced a battle with numerous players for a second US PGA title.
The Open Champion started with two pars before three-putting the third to drop back into a tie for the lead with Wiesberger and Phil Mickelson, who had birdied the first and third.
That soon became a five-way tie when Fowler recovered from a bogey on the second with birdies at the third and fourth and Stenson picked up his third shot of the day on the fifth.
But Fowler, who finished joint fifth in the Masters Tournament and joint second in the US Open and Open this season, then moved into the outright lead by chipping in for his third birdie in succession on the fifth.
The greens had dried remarkably well thanks to a special drainage system and the course was vulnerable to low scores, with Ernie Els threatening to post the first sub-63 score in Major Championship history.
Els raced to the turn in 30 with four birdies in a row from the third and another on the ninth, the four-time major winner then making a birdie on the 11th to move to 11 under par.
McIlroy was looking to claim the fourth Major of his career and become the first player since Padraig Harrington in 2008 to win back-to-back Majors.
Lifting the Wanamaker Trophy for the second time would also see the Northern Irishman become the third youngest player after Tiger Woods and Jack Nicklaus to win four Majors, just one less than the total won by the late Seve Ballesteros and two behind Sir Nick Faldo.
Stenson joined Fowler in the lead when he two-putted the par five seventh and the World Number Four then made an excellent par save from a greenside bunker on the eighth.
But McIlroy continued to go in the wrong direction, failing to get up and down from sand on the sixth to fall two shots off the pace.
Els' bid to make history came to an end with a run of five straight pars before a bogey on the 17th, but the 44 year old birdied the last to card a 65 that was matched by playing partner Jimmy Walker.
That set the clubhouse target at 11 under par but did not look enough to win as Fowler birdied the seventh and Stenson the ninth to move to 14 under.
Mickelson narrowly missed an eagle putt on the seventh but a birdie kept him just one behind Fowler, while McIlroy picked up his first birdie on the same hole to get within two of the lead.
