Lavanini gets first Jaguares start
Lavanini's inclusion is one of seven changes to the starting line-up that did duty against the Force two weeks ago.
In the forwards, Lucas Noguera and Leonardo Senatore return to the starting XV in place of Santiago Garcia Botta and Benjamín Macome.
There are wholesale changes to the backline as Nicolas Sánchez, Matías Orlando, Jerónimo De la Fuente and Ramiro Moyano replace Juan Martín Hernández, Santiago Gonzalez Iglesias, Matías Moroni and Santiago Cordero.
The Brumbies currently top the Australian Conference on 23 points while the Jaguares, who are third on the South Africa Two Conference, have one point more.
It will be the first match between the sides in the history of the competition.
Jaguares: 15 Joaquin Tuculet, 14 Ramiro Moyano, 13 Matias Orlando, 12 Jeronimo de la Fuente, 11 Bautista Ezcurra, 10 Nicolas Sanchez, 9 Martin Landajo, 8 Leonardo Senatore, 7 Juan Manuel Leguizamon, 6 Tomas Lezana, 5 Tomas Lavanini, 4 Matias Alemanno, 3 Ramiro Herrera, 2 Agustin Creevy, 1 Lucas Noguera.
Replacements: 16 Julian Montoya, 17 Santiago Garcia Botta, 18 Enrique Pieretto, 19 Guido Petti, 20 Javier Ortega Desio, 21 Gonzalo Bertranou, 22 Juan Martin Hernandez, 23 Matias Moroni.
Date: Saturday, May 27
Venue: Vélez Sarsfield, Buenos Aires
Kick-off: 18.40 (21.40 GMT; 07.40, Sunday, May 28 AEST)
Referee: Mike Fraser
Assistant referees: Federico Anselmi, Jose Covasi
TMO: Santiago Borsani
