Dufner finished the day with a score of 63, breaking the course record at Oak Hill Country Club and tying the record for the lowest score in any of golf's four majors.
Dufner is sitting at the top of the leaderboard at -9. He seeks his first major championship here in Rochester, NY.
He had a chance at the first 62 in major championship history, but left a birdie putt at 18 short.
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