Coach Felipe Contepomi on Thursday announced four changes in the starting line-up to the team who lost 20-19 against the Wallabies in La Plata last Saturday, when Argentina gave away a late penalty and were beaten by a last-gasp kick.
Petti and Lavanini both came off the bench last weekend as Argentina struggled to dominate the set pieces and rucks in rainy conditions.
It was Petti's first Test for Argentina this year and his return to the starting line-up comes at the expense of Franco Molina while Lavanini replaces Pedro Rubiolo, who suffered a concussion in the opening minute of last weekend's match.
Reliable kicker Santiago Carreras is replaced at flyhalf by Tomas Albornoz while Bautista Delguy comes in on the right wing in place of Santiago Cordero in the other changes for a fourth match in this year's southern hemisphere championship for both teams.
Saturday's Test in Santa Fe will mark Argentina skipper Julian Montoya's 100th cap.
Gonzalo Garcia keeps his place as backup scrumhalf after Lautaro Bazan Velez picked up an injury in the warm-up last Saturday.
Argentina surprised with a call-up this week for 35-year-old Tomas Cubelli, who looked to be the preferred cover for first choice Gonzalo Bertranou. But no sooner had Cubelli joined the camp he suffered a muscle strain.
Argentina and Australia have both lost two of their opening three matches in this year's competition.
Argentina: Juan Cruz Mallia, Bautista Delguy, Lucio Cinti, Santiago Chocobares, Mateo Carreras, Tomas Albornoz, Gonzalo Bertranou, Juan Martin Gonzalez, Marcos Kremer, Pablo Matera, Tomas Lavanini, Replacements: Ignacio Ruiz, Mayco Vivas, Eduardo Bello, Franco Molina, Joaquin Oviedo, Santiago Grondona, Gonzalo Garcia, Santiago Carreras.
