Oakland won for just the second time in eight games, a struggling stretch that has followed four straight wins.
Jed Lowrie hit a three-run blast in the Oakland first and Yoenis Cespedes followed with a solo shot later in the inning. The Athletics built a 6-3 lead through two innings before Reddick began his assault.
Reddick hit solo homers in both the third and fifth innings before unloading with a three-run shot in the sixth.
Oakland pounded out 17 hits to make things easy for Jarrod Parker (8-6), who picked up the win by limiting Toronto to three runs on six hits in six innings.