River Plate, despite beating their Brazilian opponents 2-0 in the second leg, could not turn around the first leg's 3-0 defeat.
Robert Rojas opened the scoring for the Argentinians in the 29th minute, and before the first half ended, Rafael Santos Borre doubled the lead.
In the second half, all River Plate needed was another goal to at least play an extra time, but it did not happen. Rojas was sent off in the 73rd minute after receiving a second yellow card.
Palmeiras will either play Boca Juniors or Santos in the Libertadores Cup final, which is South America's equivalent of Europe's Champions League.
