Dufner fired a 7-under-par 63, which moved him into the lead of the 95th PGA Championship in Pittsford, N.Y. He had an iron shot for an eagle on the second hole and added five birdies after that in a bogey-free round.
Simpson had tied the record set by Ben Hogan in 1942 and matched by Curtis Strange in 1989. Hogan won the Rochester Open and Strange took the 1989 U.S. Open after their 64s at Oak Hill.
After a par at the first hole, Simpson ran off four birdies in a five-hole span to get to 7-under on the day. A bogey at the par-4 seventh hole and two closing pars gave him a share -- if short-lived -- of the course record.
Simpson was 5-over after eight holes in Thursday's first round with a front nine that included five bogeys and a double-bogey 6 at the fifth hole. But he was 3-under on his second nine of the first round. He is 9-under for his last 27 holes.
His 36-hole total of 4-under 136 is five strokes back of Dufner.
Dufner played in one of the later groups Friday and conditions were ripe for low scores. After the eagle at No. 2, he had back-to-back birdies at Nos. 4 and 5. He added back-nine birdies at 11, 13 and 16, closing with two pars to preserve the record round.