Marcelo Gallardo's River drew 1-1 in Colombia after trailing by a goal at half-time in the first leg, and the Argentine club will be confident they can build on their away goal to lift the Copa Sudamericana for the first time.
Nacional led at the break in Medellin on December 3 thanks to Orlando Berrio's goal but River ensured they will enter Wednesday's second leg at the Estadio Monumental as favourites when Leonardo Pisculichi equalised after good lead-up work by Teofilo Gutierrez.
"National [had the] advantage of the spaces in the first half but in the second [we were] smart and had the ball," River defender Leonel Vangioni said at a media conference on Friday.
Vangioni called on his team-mates to make the most of their opportunity, as River look to win their first major continental title since the 1996 Copa Libertadores.
"We are 90 minutes from achieving something very important for the club and for us," he said.
While River are the leading scorers in the Copa Sudamericana with 15, it could be their defensive record at home that will decide the second leg.
River have kept clean sheets in three of their four home legs in the 2014 tournament, although Nacional have generally done well on the road, winning three of five this year including two 1-0 victories.
Luis Ruiz and Edwin Cardona will be Nacional's main men in front of goal with both having struck three times in South America's second tier continental club competition this season, although neither is in great form.
Ruiz has not scored in three games in all competitions for the Colombian club, while Cardona has failed to hit the back of the net in four matches for Nacional.
River's Uruguayan striker Rodrigo Mora (four goals) will be the hosts' leading option up front, while Pisculichi will pull the strings for the hosts having notched three assists in the competition.
The visitors will arrive in Buenos Aires also aiming for their maiden Copa Sudamericana triumph, having lost the final in 2002 although they have previously won the Libertadores in 1989.
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