Argentina topped Group C courtesy of the narrow victory on Thursday night.
Mascherano scored the crucial goal 12 minutes from the end as Alfio Basile's men recorded their third consecutive victory in South America's showpiece tournament.
Argentina will now return to Barquisimeto on Sunday to take on the Peruvians, while Paraguay face Mexico in Maturin on the same day.
Meanwhile, Colombia claimed their first victory as Jaime Castrillon headed the only goal of the game to overcome the United States 1-0 in Barquisimeto.
Neither side had claimed a point before the encounter and were playing for little more than pride but it was the South Americans who took all three points to leave a young, inexperienced USA side propping up the group in stark contrast to their triumphant Gold Cup campaign just under two weeks ago.
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