[1] He officiated his first CONMEBOL club fixture on 11 August 2016 in the Copa Sudamericana in a match between Sol de América of Paraguay and Jorge Wilstermann of Bolivia.

[4] Ostojich officiated his first senior international fixture on 16 November 2018, a friendly match between Argentina and Mexico.

[5] The following year, he was selected as a referee for the 2019 Copa América in Brazil,[6] where he officiated a group stage match between Bolivia and Venezuela.

[8][9][10] He was appointed as a VAR for the 2019 FIFA Club World Cup in Qatar,[11][12] and was assigned to three matches including the final between Liverpool of England and Flamengo of Brazil.

[13][14][15] For health reasons, Ostojich replaced his compatriot Leodán González as a referee at the 2020 FIFA Club World Cup, held in February 2021 in Qatar.