Early starters faced receptive, rain-softened conditions in the PGA Championship third round on Saturday and former U.S. Open champion Justin Rose was among those who took advantage.
The English world number five, who made the cut by just one shot, birdied four of the first seven holes to reach the turn in four-under-par 31 on a damp, muggy and mainly overcast day at Valhalla Golf Club.
Wielding a red-hot putter, Rose drained 30-footers at the first and third before driving the green at the par-four fourth and two-putting for his third birdie of the day.
He picked up another shot at the par-five seventh where he again drained a monster putt, this time from 32 feet.
Rose, who won his first major title at last year's U.S. Open, then sank a 16-foot birdie putt at the par-four 13th to get to five under for the tournament, four strokes behind overnight leader Rory McIlroy.
Northern Irishman McIlroy, who is bidding for his fourth major crown and a third consecutive victory on the PGA Tour, was scheduled to tee off at 3 p.m. ET in the company of Australian Jason Day.
World number one McIlroy, who has produced spectacular form over the past month, seized a one-shot overnight lead after carding a second-round 67 on a wet, ultra-long Valhalla layout.
The 25-year-old was an overwhelming favorite heading into the year's final major, having completed a wire-to-wire victory at last month's British Open before winning the WGC-Bridgestone Invitational last Sunday in his next start.
So far, he has fully justified that billing in posting a 36-hole total of nine-under 133, leaving the rest of his rivals to play catch-up over the last two rounds.
Day, seeking his first major title, was tied for second with veteran American Jim Furyk at eight under, with Finland's Mikko Ilonen and Americans Rickie Fowler and Ryan Palmer a further stroke back in fourth.
Fourteen players were bunched within four shots of the lead heading into the second round, including five-times major champion Phil Mickelson of the United States and England's former world number one Lee Westwood.
Conditions were expected to remain wet on Saturday with possible thunderstorms forecast for later in the day.