McGirt, who has never held a piece of a second-round lead in his PGA Tour career, carded a birdie on No. 15 to jump into a share of the top spot at 11-under 129.
Piercy registered a 3-under 67 following Thursday's course-record 62 to keep pace with McGirt atop the leaderboard at Hamilton Golf & Country Club.
Claiming sole possession of third place one shot back was Robert Garrigus, who carded a 4-under 66.
Bo Van Pelt, who sank an eagle on the final hole for a 66, was fourth at 9-under.
Exploding whale video goes viral on Internet
Caroline Berg Eriksen: Soccer player's wife triggers debate with post-birth selfie