Ignacio Scocco's first-half tally stood up as the match winner on Sunday as 10-man Newell's climbed to within three points of the top spot in Argentina's top flight after posting a 1-0 win over River Plate.
Scocco gave Newell's the advantage in the 35th minute and the club stepped up defensively when Gerardo Martino was sent off with nine minutes to play to hold on for the victory.
Newell's has won four of its first six matches to collect 13 points, while River Plate remains one point behind Newell's in third place through six matches.
Elsewhere in the Argentine Clausura on Sunday, Carlos Izquierdoz scored the only goal of the match in a 1-0 win for Lanus over Godoy Cruz, while Jorge Velazquez and Mauro Camoranesi exchanged goals in a 1-1 draw between Belgrano and Racing.
Leandro Bentez scored a late equalizer in the 78th minute to rescue a point for Estudiantes in a 1-1 stalemate with Velez Sarsfield, while Boca Juniors and Argentinos Juniors capped Sunday with a 1-1 draw.
Saturday's action saw a 74th-minute own goal from Ruben Ramirez lift San Lorenzo to an unorthodox 1-0 victory over Colon, while Independiente and Quilmes battled to a 1-1 draw.
Andres Franzoia scored on each side of halftime on Friday to hand Union a 2-1 triumph over Tigre, while Monday's action saw All Boys pick up a 2-1 win over Atletico Rafaela and Arsenal earn a 3-2 victory over San Martin.