[1] She then turned to voice studies at the Music Conservatory in Cluj-Napoca, before winning a scholarship at the Conservatorio di Santa Cecilia in Rome to be taught canto by Jolanda Magnoni; she also worked with Rodolfo Celletti and Elisabeth Schwarzkopf.

[3] She appeared at the Maggio Musicale Fiorentino first as Violetta in Verdi's La Traviata, directed by Visconti and conducted by Thomas Schippers, a role she reprised over 200 times.

[1] Nicolesco made her debut at the Metropolitan Opera in New York City in 1978 as Nedda in Leoncavallo's Pagliacci, a role she performed there until 1986, followed by Verdi's Violetta and Gilda in Rigoletto.

[1][5] She interpreted a wide repertoire from Baroque, belcanto, verismo and contemporary music,[1][6] and has been described as "an arresting personality with a vibrant voice";[2] highlights were the roles of Marzelline in Beethoven's Fidelio, Mozart's Elettra in Idomeneo and Vitellia in La clemenza di Tito, the title roles of Bellini's Beatrice di Tenda, Donizetti's Anna Bolena, Maria di Rohan and Maria Stuarda, Queen Elizabeth I in Roberto Devereux, Verdi's Luisa in Luisa Miller, Amelia in Simon Boccanegra, Leonora in Il trovatore and Desdemona in Otello, Marguérite in Gounod's Faust, Tatyana in Tchaikovsky's Eugene Onegin, Liù in Puccini's Turandot, and Zarina Marina in Dvořák's Dimitrij.

[7] She appeared in productions directed by Giorgio Strehler, Patrice Chéreau, Luca Ronconi, Jean-Pierre Ponnelle, Franco Zeffirelli, Pier Luigi Pizzi, Jonathan Miller and conducted by Colin Davis.

Carlo Maria Giulini, Peter Maag, Lorin Maazel, Riccardo Muti, Seiji Ozawa, Giuseppe Patané, Georges Prêtre, Gennady Rozhdestvensky, Wolfgang Sawallisch and Alberto Zedda.

She presented for the International George Enescu Year, proclaimed by UNESCO in 2005, the composer's complete songs for the first time in Japan, at Aichi World Exhibition as well as in Nagoya and Tokyo, in Prague, Paris, Rome and New York City.