The match marked Gabriel Heinze's return to Newell's, 15 years after the defender departed for a successful career in Europe, where he played for several top sides including Paris St Germain, Manchester United, Real Madrid and Marseille.
Paraguay defender Martin Caceres headed Newell's ahead after 14 minutes but they had defender Victor Lopez sent off for a wild two-footed lunge at an opponent in the 21st minute.
Heinze was brought on at that point to bolster the defence.
Martino, who took Paraguay to the World Cup quarter-finals in 2010, was then dismissed for persistent dissent on the touchline.
Newell's were not finished, however, and in the 71st minute, Scocco produced a stunning strike as he flicked the ball past a defender and hit a rising 30-metre shot into the top corner from a seemingly impossible position near the touchline.
The win left Newell's as one of five teams on seven points from three games at the top alongside Racing Club, Quilmes, Colon and Godoy Cruz.