He joined the staff of the Metropolitan Opera in New York City, where he debuted conducting Verdi's Don Carlos, on April 9, 1952, with Jussi Björling, Eleanor Steber and Regina Resnik in the cast.
In 1954, he conducted La forza again (now with Nelli and Leonard Warren), and a double-bill of Mascagni's Cavalleria rusticana and Leoncavallo's Pagliacci.
In 1954, Cellini was appointed General Director and Conductor of the New Orleans Opera Association, where he debuted with Puccini's La bohème (staged by Armando Agnini).
These young singers included Harry Theyard, Mignon Dunn, Norman Treigle, John Reardon, Audrey Schuh, André Turp, Chester Ludgin, John Macurdy, Stanley Kolk, Ara Berberian, Enrico di Giuseppe, Ticho Parly and Benjamin Rayson.
While in New Orleans Cellini conducted performances of many operas, including Verdi's Otello (with Ramón Vinay and Nelli), Puccini's Tosca (with Inge Borkh and Robert Weede), Lakmé by Delibes, Barber's Amelia al ballo (with Schuh), Elektra by R. Strauss, L'amore dei tre re, Verdi's Falstaff (with Warren), Massenet's Werther, Rossini's La cenerentola, Mussorgsky's Boris Godunov (with Boris Christoff), Verdi's Il trovatore, Puccini's Turandot, Bellini's Norma, Mozart's Don Giovanni (with Treigle), Wagner's Tannhäuser, Ponchielle's La Gioconda, Massenet's Manon (with Phyllis Curtin and Nicolai Gedda), Un ballo in maschera, Gluck's Orfeo ed Euridice, Der Rosenkavalier by R: Strauss, Rigoletto (with Cornell MacNeil) and La forza del destino (with Eileen Farrell and Richard Cassilly).