The former Liverpool and Atletico Madrid midfielder, back at his first club after a decade in Europe, raced to the far post to head a cross from the right flank beyond goalkeeper Marcelo Montoya.
Victory lifted Newell's two points ahead of Racing Club and keeps it unbeaten through 10 games of the season.
Belgrano Cordoba climbed two places to third and nudged its vanquished opponent Boca Juniors down one to fifth after a 3-1 home win.
Boca went ahead after four minutes as Santiago Silva sprinted through to finish well, but Sergio Rodriguez levelled by turning in a free-kick from 10 yards in the 23rd minute.
Victor Aquino headed Belgrano in front two minutes into the second half, before Guillermo Farre fired the third in the 70th minute, a minute after Boca had substitute Christian Cellay sent off.
River Plate enjoyed a 5-0 win over mid-table rival Godoy Cruz, featuring two spectacular strikes.
Martin Aguirre put River Plate ahead after nine minutes with a close-range finish, before, three minutes later, Leonardo Ponzio scored direct from a free-kick 35 yards out from goal. Ponzio looked set to swing over a cross from his position to the left of goal, but instead sent the ball floating over Nelson Ibanez.
Carlos Sanchez and substitute Rogelio Mori stretched the lead, before Sanchez applied the finishing touch in the 76th minute with an elegant chip into the left corner from 25 yards.
Luciano Leguizamon and Osmar Ferreyra scored in Independiente's 2-0 home win over Atletico Rafaela.