Sacchini was 25 when Durante died in 1755. The following year, he became a "mastricello" (a junior teacher in the school) and had the opportunity to compose, as the final exercise of his studies, his first operatic work, an intermezzo in two parts entitled "Fra' Donato". It was performed to great acclaim by the school's students and was followed a year later by another intermezzo, "Il giocatore". The warm reception these works enjoyed paved Sacchini's way to commissions from the smaller theatres which performed opera in Neapolitan dialect. One of his major successes was the "opera buffa" "Olimpia tradita" (1758) at the Teatro dei Fiorentini, which led to commissions from the Teatro San Carlo, where his first "opera seria", "Andromaca", was premiered in 1761. Meanwhile, Sacchini was pursuing his career at the Conservatorio, where he had initially taken up the unpaid position of "maestro di cappella straordinario", assisting the "primo maestro", Manna, and the "secondo maestro", Gallo. When Manna retired in 1761, shortly before the premiere of "Andromaca", Sacchini was promoted to "secondo maestro".