Uruguayan striker Rodrigo Mora stepped up in the absence of star man Teofilo Gutierrez, netting a brace as River accounted for Tigre 2-0 at the Estadio Monumental Antonio Vespucio Liberti on Sunday.
River have collected 16 points from six matches to move three clear of Velez Sarsfield, who played out a goalless draw with third-placed Newell's Old Boys on Saturday.
Mora, who had only netted one goal prior to Sunday's fixture, opened the scoring in the 38th minute from the edge of the area.
Mora doubled the hosts' advantage three minutes after half-time, when he coolly controlled the ball between two defenders and fired beyond Garcia once again.
Boca's resurgence under Arruabarrena continued on Sunday following their narrow 1-0 win at nine-man Olimpo.
The Argentine powerhouses had lost three of their opening four games prior to Arruabarrena's arrival, but Boca have now won back-to-back matches with the former defender at the helm.
In other results, Independiente joined Newell's on 12 points after edging 10-man Banfield 1-0 on Saturday.
Banfield were forced to play with a man less from the 34th minute following Lihue Prichoda's dismissal and it took its toll as Federico Mancuello scored the winning goal on the hour-mark.
Silvio Romero scored twice for Lanus, while Racing's goalscorer Ricardo Centurion was sent off in the 87th minute.
