Not the cleanest example, but Hearns beat Leonard (the "draw" from II) - Leonard beat Hagler - Hagler beat Hearns A better one is Hearns beat Duran - Duran beat Leonard - Leonard beat Hearns
How about... Archie Moore beating Joey Maxim - Joey Maxim beating Floyd Patterson - Floyd Patterson beating Archie Moore
This is not a very good example. Ezzard Charles beat a retired Joe Louis coming back after over 2 years away from the ring. By all accounts Walcott actually beat Louis in their first fight. Even Louis thought so. Charles had already beaten Walcott twice before Walcott managed to return the favor.