Saturday's trouble, on the second weekend of the Clausura championship, raised fears that the tournament could be blighted by the same problems as the Apertura, held in the second half of last year.
That tournament was plagued by unprecedented crowd violence, threats and initimidation.
There has already been trouble in the week since the Clausura got under way.
Last Sunday, River's match at home to Lanus was preceeded by fighting involving rival factions of the River supporters in the club's social area.
Families who had come to use the swimming pool and barbecue area were intimidated during the violence.
Last week, the directors of Quilmes and Banfield both said they had been threatened for refusing to provide their respective clubs' own supporters with free tickets and money to travel to away games.
On Thursday, 50 fans were injured during clashes before a third division game on the outskirts of Buenos Aires.
On the field, both River goals were set up by midfielder Fernando Belluschi and converted by striker Ernesto Farias.
In the 25th minute, Belluschi found Farias with a crossfield ball, the Newell's defence was slow to react and Farias fired past Justo Villar.
Nicolas Spolli popped up at the far post to equalise on the stroke of half-time but River regained the lead in the 70th minute when Farias scored from Belluschi's corner.
In other Saturday games, titleholders Estudiantes were held to a goaless draw away to Gimnasia-Jujuy and have four points from their opening two games.
Estudiantes extended their unbeaten run to 15 games but were given a let-off in the 18th minute when Hector Silva missed a penalty for Gimnasia, blasting his effort against the post.
Arsenal won their second straight game when they beat Godoy Cruz 2-1 with goals from Jorge Ortiz and Andres San Martin.
Jose Devaca replied for the Mendoza-based team.