His 63 broke the course record at Oak Hill held by Ben Hogan, Curtis Strange and Webb Simpson, who shot 64 about five hours earlier. Dufner became the 24th player to shoot 63 in a major — Greg Norman and Vijay Singh, both in the Hall of Fame, did it twice.
And through it all, Dufner barely cracked a smile.
"He's very calm," said Steve Stricker, who had been the last guy to shoot 63 in a major and, in an interesting twist, played alongside Dufner the first two days. "I'm sure he was churning on the inside."
The possibilities were endless on Friday, which began with three hours of a steady rain until the sun broke through and took all the bite out of Oak Hill.
Simpson also had a chance at 63 until he made a bogey on the 16th hole of his round. U.S. Open champion Justin Rose shot 29 on the front nine. When the second round finally ended, 27 players remained under par — this on a course that is stubborn when it comes to red numbers. In five previous majors at Oak Hill, only nine players have finished the tournament below par. Jack Nicklaus did it twice.
For all the low scores, Woods and Phil Mickelson were left behind.
Woods couldn't get anything going Friday, exchanging birdies with bogeys during a poor putting round that led to a 70 and a 1-over 141 midway through the tournament.
"Obviously, I'm going to have to put together a really good weekend," Woods said. "It's definitely gettable. Got to hit the ball in play and keep the ball near the hole so I can be aggressive with my putts."
Mickelson's swing apparently went missing in the three weeks since he won the British Open. He was all over Oak Hill again on Saturday, making a triple-bogey at the seventh hole to drop 14 shots behind Dufner, who was still hours from teeing off.
Dufner's popularity has grown since April, when someone took that photo of him during a charity event as the teacher taught children how to relax and concentrate.
He embraced the craze, which seems to fit perfectly with his laid-back approach.
But there were nerves, no doubt, and Dufner showed them at the very end of the second round.
"It's tough when you're chasing history," he said. "You will be the first one to do something. I don't think I've been the first to do anything in my life. So it was a little nerve-racking for a Friday. It's usually the pressure you might feel toward the end of the tournament."
That part is still to come.
Scott, playing in the final group with Dufner on Saturday, was in the hunt on the weekend for the fourth time in the last six majors. Henrik Stenson, a runner-up at Muirfield, had a 66 and joined Rose at 134, only three shots behind. Stricker and Robert Garrigus were another shot back.
After his historic round, Dufner gave up his cap, shirt and glove to the PGA for its museum.
The prize he really wants is the Wanamaker Trophy.
"I'm looking forward to a good weekend," Dufner said, "and maybe closing one of these out."