Close to 50,000 fans packed into Boca's famous home venue to see their heroes ahead of the final leg, with officials eventually cutting off stadium access to avoid overcrowding.
The first leg saw Boca come from behind twice to end 2-2 at the La Bombonera last weekend, giving River Plate a minor advantage with this weekend's decider to be played at their El Monumental stadium.
Boca have previously had a policy that only allows club members to attend the stadium, which meant the open training session was an opportunity for many people to visit La Bombonera for the first time.
Boca will be hoping to win their seventh Copa Libertadores title - their first since 2007 - while River Plate have won the competition on three occasions with the 2015 edition their most recent triumph.
