Argentina, a two-time Olympic men’s soccer champion, was defeated 2-0 by Australia in their opening game at the Tokyo Games on Thursday.
Australia took the lead in its first Olympic game since 2008 with a tap-in from Lachlan Wales in the 14th minute at the Sapporo Dome.
Marco Tilio scored the game-winning goal in the 80th minute, just a minute after coming off the bench.
Australia leads Group C, followed by Egypt and Spain, who drew 0-0 in the other game.
Argentina won Olympic gold medals in 2004 and 2008.
Australia’s best finish was fourth in 1992.