Webb Simpson was 5-over par through eight holes on Thursday, but rallied to shoot 72. He continued that rally on Friday.
The 2012 U.S. Open champion mixed seven birdies and a lone bogey in a round of 6-under 64 on Friday. Simpson matched the course record on Oak Hill's East Course.
Simpson matched the mark set by a couple of World Golf Hall of Famers -- Ben Hogan in 1942 and Curtis Strange, who matched the record in 1989.
"I wasn't aware that 64 was the course record, but I was thinking about the major championship record. I wasn't sure if it was 63, I thought it was, so I was thinking about that coming down the last few holes," Simpson admitted. "It was playing long, nothing was easy. I think the only thing the rain made it easier was the greens were softer so you could be a little more aggressive with your irons shots."
On Friday, Simpson started on the 10th and collected birdies on his first two holes. After a pair of pars, Simpson birdied the 14th to move to minus-3 for the day and 1-under par for the championship.
Simpson gutted out five straight pars in the worst of the morning rain. He soared into contention with back-to-back birdies from the second, and again from the fifth.
Standing at 5-under for the championship after four birdies in a 5-hole span, Simpson tripped to a bogey at the seventh. He closed with a pair of pars to post 64.