Racing Club and Emelec both advanced to the Copa Libertadores quarter-finals on Thursday, while the Superclasico between Boca Juniors and River Plate was suspended.
As River's players made their way onto the pitch after half-time at La Bombonera, around six seemed affected by some form of irritant - potentially pepper spray or tear gas.
Leading 1-0 on aggregate following their win at home last week, River's players and staff were understandably unwilling to proceed following the apparent attack from the fans of their archrivals.
After a delay of over an hour in Buenos Aires, the match was eventually suspended, although it remains unconfirmed whether River will advance to the last-eight automatically.
In the later match, Atletico Nacional defeated Emelec 1-0 in Colombia but the Ecuadorians held on for a 2-1 aggregate victory despite losing Pedro Quinonez to a red card three minutes before half-time.
Alexis Henriquez scored just after the hour-mark for Atletico with a powerful header from Jonathan Copete's cross but it was not enough to overhaul Emelec's lead from the first leg.
Earlier, Racing defeated Wanderers 2-1 in Argentina to progress 3-2 on aggregate.
The home side had the tie effectively wrapped up in the closing stages with Washington Camacho and Gustavo Bou having scored in the first half, and although Maximiliano Olivera hit back for Wanderers in the 89th minute it was not enough for the Uruguayan visitors.
The final spot in the Copa Libertadores' last-eight will be decided when CONMEBOL - South America's football governing body - decides how to proceed with the tie between Boca and River.
Cruzeiro, Tigres UANL, Santa Fe, Internacional, Guarani, Racing and Emelec have confirmed their progress.
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