McIlroy chases history with foes in hot pursuit
Rory McIlroy watches his tee shot on the 10th hole during the second round of the PGA Championship in Louisville, Kentucky, on August 8, 2014 - by Andrew Redington
The 25-year-old Northern Irishman could become the fourth-youngest player to win a fourth career major after Young Tom Morris, Tiger Woods and Jack Nicklaus.
He would be the first man since Padraig Harrington in 2008 to win two majors in the same year and two in a row, the Irishman having taken the British Open and PGA titles six years ago.
"It would be big," McIlroy said. "There's a lot of golf left to play and I'm going to try my best to just keep what I've got and keep doing that.
"If I was sitting right here on Sunday night with the Wanamaker Trophy I would be very happy."
Coming off his third major victory last month at the British Open and a victory last week in a warm-up event for the year's last major event, McIlroy stood on nine-under par 133 after 36 holes.
"I'm confident and just on a good run," McIlroy said.
"I'm very pleased. I'm in a great position going into the weekend in another major championship. Can't ask for much more."
McIlroy could also become only the 11th player, and the first since Tiger Woods in 2007, to win a major the week after winning another title.
Hot on McIlroy's heels in the hunt for the $1.8 million (1.34 million euro) top prize at the $10 million (7.45 million euro) event were a mix of young stars, major winners and veterans hungry for their first major crown.
Australian Jason Day, whose five top-five major finishes without a win include three runner-up efforts, and 44-year-old American Jim Furyk, last year's PGA runner-up whose lone major win came at the 2003 US Open, shared second on 134.
Another stroke adrift are Americans Rickie Fowler and Ryan Palmer and Finland's Mikko Ilonen with five-time major champion Phil Mickelson and Austrian Bernd Wiesberger on 136.
US and British Open runner-up Fowler, who finished joint fifth at this year's Masters, could become the first top-five finisher at all four majors in one year since Tiger Woods in 2005.
Woods, a 14-time major champion, missed the cut Friday after battling through the second round with back pain.
England's Lee Westwood, eight times a top-three major finisher without ever winning, was in a pack four strokes off the pace that also included 2010 British Open winner Louis Oosthuizen of South Africa and fourth-ranked Swede Henrik Stenson.
Rain that soaked the course Friday returned to greet the early starters in round three with forecasters predicting a chance of afternoon thunderstorms and McIlroy starting with Day in the last pairing at 3 p.m. (2000 GMT).