MADISON, Mississippi, July 20, 2012 (AFP) - Horschel made a pair of eagles on number five and number 18 holes in his bogey-free round to reach a 13-under 131 total.
Matt Bettencourt was one stroke back after a six-under 66. First-round leader Jason Bohn must finish his round Saturday morning. He is 12-under through the front nine.
It was a tiring day for Horschel, who played 31 holes of golf Friday. He battled through a one-hour rain delay in the morning and blistering heat later in the day.
The 25-year-old finished his first-round early Friday after heavy rains ended Thursday's round.
Close to half the field will need to finish the second round on Saturday.