He conducted the first performances of two Wagner operas : Tristan und Isolde ( 1865 ) and Die Meistersinger von NÃ 1\/4 rnberg ( 1868 ) . He conducted the premieres of two Wagner operas , Tristan und Isolde and Die Meistersinger von NÃ 1\/4 rnberg , in 1865 and 1868 respectively ; both were immensely successful .