Guerrero Jr. crushed his second homer of the season, a moonshot hit out of the Pawtucket Red Sox's McCoy Stadium.
The home run came on the first pitch of his fourth-inning at-bat off pitcher Bobby Poyner.
Guerrero Jr. has yet to make his Major League debut with Toronto. He is working his way back after this spring he suffered an oblique injury suffered while taking a swing at the plate.
In five games with the Bisons, he is hitting .412 with two homers in 20 trips to the plate.