Thursday's Copa Libertadores match between the two turned to chaos when Boca fans apparently cut an opening in a tunnel put up to protect players as they entered the field and filled it with pepper spray or mace to douse the opponents.
River players stumbled onto the field to start the second half of the scoreless match covering their faces, rubbing their eyes and dousing themselves with bottles of water.
The players then huddled together at the centre of Boca's compact La Bombonera stadium, seeking refuge alongside police and officials who waited more than an hour before suspending the game.
Trapped at the centre of the field with many of the 50,000 fans refusing to leave, players waited another hour before it was safe to move, and then sought shelter under shields held overhead by police who were battered with flying objects.
"My whole body hurts," River player Leonardo Ponzio said. "They threw — I'm not sure what it was — pepper spray at us. This just can't be."
River said in a medical statement that at least four players were diagnosed with inflamed corneas after hospital visits, and several were burned from the spray.
Once again, a soccer stadium in Argentina turned to a crime scene with Buenos Aires public prosecutor Martin Ocampo saying Friday the stadium was being sealed off to "gather evidence."
Soccer violence in common in South America and Europe. But Argentina's may be the worst.
And no game is more volatile than Boca vs. River, which ranks up there with Real Madrid vs. Barcelona for intensity. Thursday's match was also the third the clubs had played against each other in 12 days, and they each had won once.
Argentine media were calling Thursday's meeting "The Game of the Year," and it took place in the second and decisive leg of a knockout round in the Copa Libertadores, Latin America's equivalent of the Champions League.
Boca won 2-0 against its rival in the league, and then River won four days later 1-0 in the first-leg match in the round of 16 in the Copa Libertadores.
Argentina's problem is rooted in so-called "barras bravas," organized hooligan groups that have connections to clubs, powerful politicians and the police. They operate with near impunity, scalping tickets, parking cars and battling rival gangs for turf inside and outside the stadiums.
"I can't say that they (Boca) lost control with the scant information I have," Ocampo said.
Argentina already bans visiting fans from attending matches, but that has not stemmed the violence.
The Argentine Football Association has been widely criticized for failing to crack down. But they say it is a societal problem in Argentina, which is battling fierce inflation and social unrest and rising street crime.
Nestor Benitez, a spokesman for the governing body of South American football, said officials were awaiting a report from the referee and were likely to say Saturday how the suspended game would be handled.
Sergio Berni, a top Argentine national security official, but the blame squarely with Boca.
"Boca is the only one responsible, this is undeniable," Berni told reporters. "The club neglected to provide internal security."Suggest a correction