Rioting "Barra brava" hooligans caused mayhem inside and outside the giant stadium after a 1-1 draw with Belgrano in the second leg of a relegation-play-off condemned the 33-time Argentine champions to Nacional B division for next season.
The violence from the fans throwing metal bars and stones left 25 people, including six police officers, injured, with one badly hurt after being hit by a car.
A major avenue nearby looked like a war zone with bonfires blazing, shops windows smashed and stores looted.
A city prosecutor ordered the temporary closure of the stadium - exactly four weeks before it is due to stage the final of the Copa America - for an investigation into policing and possible illegal sale of extra tickets.
"We will be looking for proof that more fans got in than is authorised," prosecutor Gustavo Galante told America television, adding the limit allowed by the government for the Monumental is just over 40,000. Observers estimated the crowd at some 60,000.
Galante said his office had asked for the match to be played behind closed doors after an invasion of the pitch by River fans in Cordoba that interrupted the first leg for 20 minutes.
Players of both sides had to leave the Monumental pitch under the protection of stewards while police used high power hoses and tear gas to try to disperse the rioting fans.
Belgrano were later able to celebrate promotion with the few hundred visiting fans, who, for their safety, were kept in their sector of the stands nearly three hours after the final whistle.
SHOCK EQUALISER
Trailing 2-0 after the first leg, River were hoping for a handsome victory to save them from relegation on the 15th anniversary of their second Libertadores Cup title.
They went ahead in the sixth minute when striker Mariano Pavone controlled on the edge of the box, swivelled and shot low into the corner past diving keeper Juan Carlos Olave.
Midfielder Guillermo Farre stunned the crowd when he equalised just past the hour, however, blasting the loose ball past a stranded goalkeeper Juan Pablo Carrizo after a blunder in the River defence.
Olave then sealed River's fate, and his team's 3-1 aggregate victory, with a penalty save from Pavone after a push on fellow striker Leandro Caruso.
Referee Sergio Pezzotta was the butt of criticism from River fans for turning down appeals for a penalty in the first half for what looked like a blatant foul on Caruso.
Former defender Jorge Higuain told Radio Continental that River made a huge mistake 10 years ago in sacking a key figure in their successful youth scheme, Brazilian Delem who played as a forward for the club in the 1960s.
"It went downhill after they got rid of Delem," said Higuain, father of Real Madrid and Argentina striker Gonzalo Higuain, who was the last top quality player to emerge from River's junior ranks in 2004.
River, noted for the quality of their football and the players they produced - like former European Footballer
