Diego Milito's late penalty earned Racing Club a third win in four games as their strong start to the Torneo Apertura continued on Tuesday.
The former Inter Milan and Argentina striker converted three minutes from time for the game's only goal to see off Arsenal Sarandi.
Independiente staged a thrilling late comeback against 10-man Olimpo after Jonathan Blanco went from hero to villain.
Blanco's 51st-minute spot-kick gave Olimpo a lead which they held until the 88th minute - by which time he had been sent off.
The numerical disadvantage was to prove damaging as first Sebastian Penco equalised and then Federico Mancuello struck a stoppage-time winner for Independiente.
Belgrano Cordoba and Gimnasia La Plata drew 0-0 in the day's other game.