[2] Castellini began his professional career on 28 May 1965, in San Miguel de Tucumán against Domingo Gerez.

On 4 November 1972 Castellini won his first championship by beating Hector Ricardo Palleres to claim the Argentine light middleweight title.

Castellini fought for the first time outside of his native Argentina on 25 May 1974, he travelled to Monaco to beat Carlos Alberto Salinas.

It was while in Spain that Castellini challenged for the WBA and lineal light middleweight titles, then held by Jose Manuel Duran, in front of a sell out crowd of 12,000.

Although the champion rose from the canvas, he was outworked by the faster challenger and lost his title via a split decision in a fight where both boxers finished with bloody faces.