The American admitted to feeling the pressure in trying to break the course record, but tops the leaderboard on nine-under-par heading into the third round.
"I obviously had a fantastic day today in a Major championship, chased a little bit of history," Dufner told reporters. "Came up a little short on that last putt, but all-in-all I'm excited.
"It's tough when you're chasing history. 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-wracking for a Friday. It's usually the pressure you might feel towards the end of the tournament but I got through it. I made a couple of pars, and I wish I had that putt on the last hole back again."