As overnight leader Rory McIlroy prepared for a mid-afternoon tee time at the PGA Championship on Saturday (local time), the early starters took full advantage of receptive, rain-softened conditions at Valhalla Golf Club.
Attacking the pins at every opportunity, American Brooks Koepka, Spaniard Sergio Garcia and Scotland's Marc Warren fired five-under-par 66s to rocket up the leaderboard in the year's final major, all of them finishing at five-under 208.
"It was a little easier (today) just because it was soft," the 24-year-old Koepka told reporters after racking up nine birdies and four bogeys.
"You could throw darts at the pin, they (balls) weren't spinning back or they weren't going to bounce forward. If you hit a good shot, controlled the spin, you were fine. Wherever they landed is pretty much where they stopped."
Former U.S. Open champion Justin Rose, who made the cut by just one shot, also made a storming start with five birdies in his first 13 holes before losing a bit of momentum over the closing stretch.
"Some parts of the golf course are really easy out there," the English world number five said after firing a six-birdie 67 to finish at four under, five strokes off McIlroy's overnight lead.
"Getting close to the pin with your irons is easy, but that's if you catch a good lie in the fairway. Still no wind out there. Whenever you get calm conditions, providing you have good lies, guys are going to go low."
Northern Irishman McIlroy, who is bidding for his fourth major crown and a third consecutive victory on the PGA Tour, was set to tee off at 3pm (7am NZ time) in the company of Australian Jason Day.
World number one McIlroy, who has produced spectacular form over the past month, seized a one-shot lead overnight after carding a second-round 67 on a soggy, ultra-long Valhalla layout.
The 25-year-old was an overwhelming favourite heading into the PGA Championship, 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 overnight 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.
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