ASUNCION, July 18 (Reuters) - Rioting River Plate fans forced the match to be called off in the 80th minute as the Argentine team were knocked out of the Libertadores Cup by Paraguay's Libertad on Tuesday.
Libertad were leading 3-1 at home in the quarter-final second leg and 5-3 on aggregate when Chilean referee Ruben Selman abandoned play at the Defensors del Chaco stadium after River supporters clashed with riot police on the terraces.
Although the game did not officially finish, South American policy is to let the result stand when the supporters of the losing team cause the trouble.
River themselves reached the last eight after their second round second leg tie at Sao Paulo's Pacaembu stadium was called off in the 83rd minute after Corinthians fans broke down a gate and tried to invade the pitch.
River won that game 3-1 for a 6-3 aggregate victory.
Trouble began on Tuesday when a large contingent of River fans began tearing up plastic seats and hurled them at home supporters, whose contingent included a number of fans wearing the shirts of River's arch-rivals Boca Juniors.
The River supporters forced riot police to retreat against a fence and set fire to banners as the situation turned ugly before being brought under control.
By that stage, Selman had decided it was not safe for play to continue, despite angry protests from the River players who had staged a late fightback despite being reduced to 10 men.
Libertad, who held on for a 2-2 draw in Buenos Aires in the first leg played before the World Cup, when ahead in the 17th minute when Uruguayan striker Rodrigo Lopez scored with a looping far post header over goalkeeper German Lux.
Sergio Aquino added a second for the Paraguayan underdogs in the 41st minute when he connected with the rebound after Maritn Hidalgo's shot crashed off the crossbar.
Paraguay midfielder Crisitan Riveros rifled a close-range shot into the roof of the net two minutes after halftime for Libertad's third.
River, champions in 1986 and 1996, were in further trouble in the 62nd minute when captain Marcelo Gallardo received a straight red card for a two-footed lunge on an opponent.
After being repeatedly denied by Paraguay World Cup goalkeeper Aldo Bobadilla, Daniel Passarella's team pulled one back when Ernesto Farias scored at the second attempt in the 77th minute.
But a possible fightback was ended by their own fans.