An 85-year-old woman and 55-year-old man were shot when Boca Junior fans fought amongst themselves before their team's match against Argentinos Juniors on Sunday, an emergency services official said.
The woman, who had nothing to do with the supporters, was hit in the leg while the man suffered a serious head injury after he was also shot, Alberto Cresenti told the TN cable news channel.
The latest bout of Argentine football violence broke out near Boca's Bombonera stadium, situated in a working-class district just south of the centre, around four hours before kick off.
Media reports said rival factions of the Boca supporters group known as The 12 clashed in an area of fast food restaurants known as Parque Lezama.
During the fighting, at least one man opened fire and four or five shots were heard, local media said. More than 100 people were reported to be involved in the fighting. Six were arrested.
It was the second successive week that rival factions of The 12 have fought before a game. Last week, dozens were arrested during a pitched battle before the game away to Independiente.
In a separate incident on Sunday, fans of rival clubs Argentinos Juniors and Racing Club also clashed even though their teams were involved in different games.
Buses carrying supporters to their respective matches crossed paths near the centre of Buenos Aires and rivals fans pelted each other's vehicle with stones, media reports said.
Television pictures showed the buses surrounded by police cars after the road had been cordoned off. More than 100 fans were reported to have been detained.
Argentine soccer suffers from chronic violence often blamed on organised supporters groups called barras bravas.
Many groups are split into factions who fight amongst themselves and sometimes take sides with club directors in internal political disputes.
Ten days ago, the match between Godoy Cruz and San Martin-Tucuman was abandoned in the second half after home fans fought with police who tried to stop them attacking the visiting contingent.
Last November, fans of second division Chacarita Juniors hijacked two public buses, forced the passengers to get off and ordered the drivers to take them to their team's game with Talleres.
In January, a gang of around 30 men armed with guns and baseball bats invaded the headquarters of Rosario-based first division side Newell's Old Boys and intimidated staff.