Dufner equals championship best to claim halfway lead at Oak Hill

Jason Dufner raced to a course record 63 at Oak Hill to set the halfway pace.

Adam Scott acknowledges the galleries on his way to a second round 68 at a rainy Oak Hill in the second round of the PGA Championship.

U.S. Open champion Justin Rose stepped up his challenge with a superb second round 66 - coming home with six birdies.

Defending champion Rory McIlroy battled back after a poor start to this second round to keep his title defense alive.

Tiger Woods takes a big divot as he plays his approach shot to the second hole at Oak Hill on his way to a 70.

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Dufner leads

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Rory battles

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(CNN) -- Jason Dufner took advantage of soft greens and light winds to shoot a spectacular seven-under 63 at Oak Hill Friday to lead the PGA Championship at halfway.

The American's round equaled the all-time record best score in a major and left him on nine-under 131 -- two shots clear of the field.

Earlier, Australia's Adam Scott stepped up his bid to add to his U.S. Masters title with a two-under 68 to set the clubhouse pace, but in the favorable afternoon conditions Dufner overhauled him.

Scott was joined on seven under by veteran Jim Furyk and Matt Kuchar, who shot rounds of 68 and 66 respectively.

But Tiger Woods faltered in his attempt to end a five-year victory drought in the majors with a lackluster round of 70 leaving him on one-over 141 and ten shots back.

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Dufner joined 23 other players who have shot 63 in a major and came within a whisker of having the record all to himself as his birdie putt on the tough 18th came up just short.

Woods, all-time majors record holder Jack Nicklaus, defending PGA champion Rory McIlroy and the likes of Greg Norman, are among the players to also card 63s.

"That's pretty good company right there," Dufner said after his brilliant round.

Scott is shaping as his biggest challenger over the weekend, targeting a quick addition to his majors tally after his breakthrough win at Augusta.

The 33-year-old, who admitted to bitter disappointment after briefly hitting the front at Muirfield before Phil Mickelson's charge to win the recent British Open, has carred his form to the final major of the season.

"You look at a year like Phil and Tiger have had and they can both play better than me," Scott said. "But I'm putting myself in majors with a chance to win. It doesn't matter if I'm not the best player on the planet."

Mickelson, who partnered Scott, was back on two-over 142, but the third member of the group, England's Justin Rose, was also firmly in contention.

The U.S. Open champion shot six birdies to come home in 29 for a four-under 66 that left him on six-under 134.

Swede Henrik Stenson, runner up to Mickelson in the British Open, was also on that mark after a 66.

McIlroy battled to a 71 in the morning to be on level par.