After being noticed in RINGS, Arona was offered a contract to join PRIDE Fighting Championships. He started his career there strong, defeating Pancrase veteran Guy Mezger, but his victory would be a controversial one. Mezger managed to stop Arona's takedowns and landed strikes, including a glancing head kick and several punches through the guard, which forced Arona to defend; it took two rounds for the Brazilian to come back, taking down Mezger and executing ground and pound until the end of the third round. Arona won a split decision, which was disputed by some sources, including the announcers of the match.