Isgro replaces Baustista Delguy on the right wing for the clash at Sydney Football Stadium where Argentina will look to rebound from their 28-24 loss to the Wallabies in Townsville.
Contepomi has largely kept faith with the starting 15 from Townsville but has shifted Marcos Kremer to openside flanker from the blindside while promoting Joaquin Oviedo to number eight.
Juan Martin Gonzalez shifts to the blindside while Pablo Matera, who started at number eight in Townsville, will run off the bench as Argentina look for staying power to see out the match in Sydney.
Lock Guido Petty has been promoted to start with Pedro Rubiolo in the second row, relegating Franco Molina to the reserves.
Six-cap centre Justo Piccardo comes into the squad for a place on the bench along with three-cap fullback Ignacio Mendy, who replaces the dropped Benjamin Elizalde.
Argentina are fourth in the Rugby Championship, level with South Africa on five points, but can revive their title hopes with victory over the second-placed Wallabies.
Defeat without a bonus point would eliminate the Pumas from contention.
Argentina XV v Wallabies:
15-Juan Cruz Mallia, 14-Rodrigo Isgro, 13-Lucio Cinti, 12-Santiago Chocobares, 11-Mateo Carreras, 10-Santiago Carreras, 9-Gonzalo Garcia, 8-Joaquin Oviedo, 7-Marcos Kremer, 6-Juan Martin Gonzalez, 5-Pedro Rubiolo, 4-Guido Petti, 3-Joel Sclavi, 2-Julian Montoya (captain), 1-Mayco Vivas.
Replacements: 16-Ignacio Ruiz, 17-Boris Wenger, 18-Francisco Coria Marchetti, 19-Franco Molina, 20-Pablo Matera, 21-Agustin Moyano, 22-Justo Piccardo, 23-Ignacio Mendy.
