Lautaro Acosta headed in the winner just before the final whistle Sunday and Argentina's under-20 team beat Uruguay 1-0 Sunday to earn a berth at the 2008 Beijing Olympics.
With the win, Argentina's youth squad secured the last of two berths after Brazil had already locked up the other here at the under-20 South American championships.
Brazil, which qualified after Paraguay's 3-2 victory over Chile, was playing a late match Sunday in which it only needed a tie against last-place Colombia to win the under-20 South American title.
Brazil, Argentina, Uruguay and Chile have also qualified for the next under-20 World Cup in Canada.
In the Argentina-Uruguay matchup, Acosta got his goal off a corner from Maxi Moralez, after a back-and-forth game with few scoring chances.
Brazil, prior to its final match, had eight points at the under-20 championship, the same as Argentina. Uruguay finished with seven points, Paraguay with six points and Colombia had one entering its match against Brazil.