Summerhays, whose previous best finish on the PGA Tour was a tie for fourth at the 2012 Memorial, enters Sunday's final round at 19-under par, and in position for his first career win.
The Farmington native notched 10 birdies while matching the lowest third-round score in tournament history.
"I did everything really well today," Summerhays said. "I especially drove the ball very well and I hit a lot of good shots. You have to do everything really well to shoot a 62, and I was pleased with the way I hung in there."
Summerhays, who left BYU to turn pro in 2007, had five birdies on the back nine, including three straight on holes 15, 16 and 17.
David Hearn is two shots back headed into tomorrow's final round.