The Mozarts returned to Milan for Wolfgang to complete the second carnival opera, commissioned at the end of the first journey after the success of Mitridate. The text was Lucio Silla, revised by Metastasio from an original by Giovanni de Gamerra. Wolfgang found himself in the familiar routine of composing rapidly while coping with problems such as the late arrival of singers and the withdrawal of the principal tenor due to illness. Leopold reported on 18 December that the tenor had arrived, that Wolfgang was composing his arias at breakneck speed, and that rehearsals were in full swing. The first performance, on 26 December, was chaotic: its start was delayed two hours by the late arrival of Archduke Ferdinand, there were quarrels among the principal performers, and the running time was extended by the insertion of ballets (a common practice of the time), so the performance was not over until two o'clock the following morning. Despite this, subsequent performances were well received.
Leopold continued to pursue an appointment for Wolfgang by applying to Grand Duke Leopold of Tuscany, the Empress's third son. The application was strongly supported by Count Firmian, and Leopold, in a coded letter home, said he was quite hopeful. He waited through most of January and all of February for the Grand Duke's reply. The negative response arrived on 27 February. It is not known whether the Grand Duke was influenced by his mother's opinion of the Mozart family, but his rejection effectively ended Leopold's hope of an Italian appointment for Wolfgang. The Mozarts had no choice now but to return to Salzburg, leaving Milan on 4 March and reaching home nine days later. Neither father nor son visited Italy again.