All the goals came in the final 25 minutes as substitute Cristian Nunez and striker Joaquin Boghossian put Newell's two up before Ruben Ramirez pulled one back.
Banfield, who could have gone top with a victory, are two points behind co-leaders Colon and Godoy Cruz, the only remaining unbeaten teams after six matches.
Newell's, four points off the pace, have a game in hand.
All the weekend's matches in Argentina began after a minute's silence for the hundreds of people who died as a result of the earthquake in neighbouring Chile.
Struggling River Plate came from a goal down away to Gimnasia in La Plata to draw 1-1 with a stoppage-time equaliser by striker Gustavo Canales, his first goal for his new club since returning to Argentina from Union Espanola of Chile.
River's arch-rivals Boca Juniors, who have also been going through a lean spell for the last year, drew 1-1 at home to Estudiantes on Friday when striker Martin Palermo's penalty was cancelled out by an injury-time volley from Leandro Gonzalez.
Boca and River are in the bottom half of the standings as are Racing Club, beaten 1-0 at arch-rivals Independiente in their derby, the "Clasico de Avellaneda," on Saturday.
Independiente captain Dario Gandin scored from the spot after they were awarded a penalty for handball four minutes before half time.
Roberto Ayala headed against the crossbar in the second minute and fellow centre-back Lucas Aveldano crashed a shot against the bar from 30 metres in the second half for Racing, who had striker Gabriel Hauche sent off on the hour.
Independiente substitute Patricio Rodriguez was sent off for a second booking in the final minute.
Velez Sarsfield lost the chance to go top when they were beaten 3-2 at Huracan.
