The Brazilian outfit posted a comprehensive performance to record a shock 3-0 victory in the first leg and will be looking to complete the job at home.
In what was a classic case of a back-against-the-wall approach, Palmeiras were content to sit back and play on the counter. They recorded the victory despite having just 29% possession.
The pace of Rony and Gustavo Scarpa took advantage of River Plate's ridiculously high line, while the Argentines were also let down by some schoolboy defending.
River Plate seemed to suffer a psychological setback from the loss. They followed it up with a 2-0 defeat to Independiente at home in the Copa Diego Amando Maradona.
Palmeiras built on their continental win with a victory domestically, recording a 1-0 away win against Sport Recife.
Palmeiras vs River Plate Head-to-Head
Last week's meeting was the first between the two sides on the continent.
Palmeiras' victory gives them bragging rights over their Argentine rivals and one foot in the final.
Palmeiras form guide (all competitions): W-W-W-W-D
River Plate form guide: L-L- D-W-W
Palmeiras vs River Plate Team News
Star forward Gabriel Veron returned to action for the clash with Sport and assisted Willian for the winning goal before suffering an injury. The 18-year-old missed the first-leg clash and is unlikely to be available for the return leg.
Defender Luan da Silva was a late exclusion from the starting lineup in Buenos Aires due to injury. However, he started at the weekend and could be on from the start on Wednesday.
Abel Ferreira named a heavily-rotated side for the trip to Recife and will have most of his preferred squad available.
Wesley, Felipe Melo, and Jean are still ruled out, while Patrick de Paula is suspended for accumulated yellow cards.
Injuries: Gabriel Veron, Felipe Melo, Wesley, Jean
Suspended: Patrick de Paula
The visitors have Fabricio Angileri and Jorge Moreira ruled out through injury.
Midfielder Jorge Carrascal is suspended, following his red card in the first leg.
Marcelo Gallardo made several changes to his team that lost at the weekend. He is expected to field his strongest side, despite being let down by several of them in the first leg.
Injuries: Fabricio Angileri, Jorge Moreira
Suspended: Jorge Carrascal
Palmeiras vs River Plate Predicted XI
Palmeiras Predicted XI (4-2-3-1): Weverton; Matias Vina, Gustavo Gomez, Luan Garcia, Marcos Rocha; Gabriel Menino, Danilo; Willian, Raphael Veiga, Rony, Luis Adriano
River Plate Predicted XI (4-1-3-2): Franco Armani, Javier Pinola, Paulo Diaz, Robert Rojas, Gonzalo Montiel; Enzo Perez, Nicolas De La Cruz, Ignacio Fernandez, Bruno Zuculini, Rafael Santos Borre, Lucas Beltran
Palmeiras vs River Plate Prediction
Palmeiras' games tend to be low-scoring affairs and they are currently on a run of four consecutive clean sheets.
However, River Plate need to get on the scoresheet and are likely to breach Weverton's goal, while leaving space behind to be exploited.
Ultimately, the sides might cancel each other out in a score draw which will be enough for Palmeiras to secure a first Libertadores final.
Prediction: Palmeiras 1-1 River Plate