The "superclasico" is regarded by fans as the biggest event of the season and victory can make up for not lifting the title or playing badly in the rest of the matches put together, while defeat can only be cured in their next clash.
The match at River's Monumental stadium is a 53,000-capacity sellout.
The club, which has topped gate takings in the last three tournaments, sold 35,000 seats in eight hours on Tuesday before putting the "populares," tickets for the old-style standing terraces behind the goals, on sale from Wednesday.
River, at one of the lowest ebbs of their 108 years, are in dire need of a victory to pull away from the lower reaches of the Apertura championship standings. They have one win and six points from nine matches.
Boca are in better shape having overcome a poor start to the season with a run of three wins inspired by playmaker Juan Roman Riquelme, who has recovered from injury niggles to steer them into the title race.
Alfio Basile's team, in mid-table with 14 points, are five points behind leaders San Lorenzo at the halfway stage.
"Riquelme is among the three best (players) in the world. Riquelme conducts everything," former Argentina coach Basile, who nearly quit when Boca had gone six matchers with only one victory, told Radio del Plata.
TURNING POINT
Basile's team, despite playing away, are the favourites after turning the corner with a 3-2 home victory over title holders Velez Sarsfield three weeks ago.
Striker Martin Palermo, who helped to spark the revival when he headed the winner against Velez from nearly 40 metres, is determined to play despite fracturing his nose helping Argentina to beat Peru in a World Cup qualifier 10 days later.
River, traditionally a strong attacking team, have struggled since the season began, their only victory coming in August when they beat bottom team Chacarita Juniors 4-3 to notch up almost half their tally of nine in nine matches.
A change of coach two weeks ago, with one former player, Leonardo Astrada, replacing another, Nestor Gorosito, produced a slight improvement.
However, River are relying heavily on 35-year-old former Argentina midfielder Matias Almeyda, who filled in at centre back in last weekend's 0-0 draw at Huracan, to steady a young team, and on fellow 1998 and 2002 World Cup veterans Ariel Ortega and Marcelo Gallardo to create chances.
"You have to play Boca with your heart more than with your head," said Astrada, a one-club veteran who shared many Boca clashes with the trio.
"It's a match apart. It doesn't matter in what position (in the standings) either side is coming into it, what matters is to beat our eternal rivals."
