Piercy had a 6-under 66 and Kuchar a 67 to enable the two to finish 54 holes at 14-under 202.
Rod Pampling (65) and tour rookie Leif Olson (68) share third place at minus-13. Nicholas Thompson had a 69-204 Saturday for fourth place. Second-round leader Vaughn Taylor (71) is tied for sixth place with Jonathan Byrd (67), Tim Petrovic (68) and Fredrik Jacobson (69) at 11-under 205.
Saturday's third round brought the best conditions so far this week after heavy overnight rain.
"Today, with these conditions, you could attack every pin," Kuchar said. "Even if you short-sided yourself, you could place the ball in the rough, have a beautiful lie and have a pretty good chip for birdie."