It should be noted that Christ does defeat Satan but not through historic events. Christ defeats Satan only by the transforming power of his internal workings of his Spirit. This is not a historic event but a in Christ event. It is only in Christ that Satan is bound which is what the workings of the Cross is all about, to bring about new life.
Gene Fadeley
Did Christ defeat Satan? In about A.D. 58, Paul told the Roman Christians, "The God of peace will crush Satan under your feet shortly." (Rom. 16:20) Twelve years later, in A.D. 70, Satan was cast into the lake of fire and brimstone. (Rev. 20:10) His power was broken, he was rendered useless according to Bible prophecy. Satan can no longer take over a person's body and make men do anything against his will.
http://www.bibleprophecy.com/devil.html