Title: January 1900
Content: The opera Tosca, composed by Giacomo Puccini, was presented for the first time, premiering at the Teatro Costanzi in Rome. Soprano Hariclea Darclée sang in the role of Floria Tosca, and tenor Emilio De Marchi appeared as her lover, Mario Cavaradossi. 
Title: Il trittico
Content:  Around 1904, Puccini first began planning a set of one-act operas, largely because of the success of Pietro Mascagni's Cavalleria rusticana. Originally, he planned to write each opera to reflect one of the parts of Dante's Divine Comedy. However, he eventually based only Gianni Schicchi on Dante's epic poem. The link in the final work is that each opera deals with the concealment of a death. Puccini also intended that the three should be performed as a set, and wrote to Casa Ricordi to complain about their giving permission in 1920 to The Royal Opera, London, "for Tabarro and Schicchi 
Title: Gianni Schicchi
Content:  The one-act opera genre had become increasingly popular in Italy following the 1890 competition sponsored by publisher Edoardo Sonzogno for the best such work, which was won by the young Pietro Mascagni's Cavalleria rusticana. With Tosca essentially completed by November 1899, Puccini sought a new project. Among sources he considered, before proceeding with Madama Butterfly, were three works by French dramatist Alphonse Daudet that Puccini thought might be made into a trilogy of one-act operas. After Butterfly premiered in 1904, Puccini again had difficulty finding a new subject. He further considered the idea of composing three one-act operas to be performed together but found his publisher, Giulio Ricordi, firmly opposed 
Title: Il trittico
Content:  Il trittico (The Triptych) is the title of a collection of three one-act operas, Il tabarro, Suor Angelica, and Gianni Schicchi, by Giacomo Puccini. The work received its world premiere at the Metropolitan Opera on 14 December 1918.
Title: 1900 in music
Content: John Philip Sousa – Chris and the Wonderful Lamp, premiere in New York City, January 1 ; Giacomo Puccini – Tosca, premièred at the Teatro Constanzi in Rome, January 14 ; Jan Blockx – Thyl Uylenspiegel, premièred in Brussels, January 18 ; Alexander von Zemlinsky – Es war einmal, premièred in Vienna Opera, January 22 ; Gustave Charpentier – Louise, première in Paris Opera-Comique, February 2 ; Ermanno Wolf-Ferrari – La Cenerentola, première in Theatro le Fenice in Venice, February 22 ; Gabriel Fauré – Prométhée, première of his first opera in Roman arena at Beziers, August 27 ; Mikhail Ippolitov-Ivanov – Asya, première in Moscow, September 28 ; Władysław Żeleński - premiere of the opera Janek in Austria, October 4 ; Nikolai Rimsky-Korsakov – The Tale of Tsar Saltan, première in Solodovnikov Theatre in Moscow, November 3 ; Ruggiero Leoncavallo – Zaza, première in Teatro Lirico in Molan, November 10 ; George Stephanescu – Cometa ; César Cui – Feast in Time of Plague, première in Moscow at the Noviy Theater, November 1901 
Title: Turandot
Content:  on traditional Chinese music and anthems, and the melody of a Chinese song "Mò Li Hūa (茉莉花)", or "Jasmine", became a motif for the princess. Puccini left the opera unfinished at the time of his death in 1924; Franco Alfano completed it in 1926. The first performance took place at the Teatro alla Scala in Milan on 25 April 1926, conducted by Arturo Toscanini. The performance included only Puccini's music without Alfano's additions. The first performance of the opera as completed by Alfano was performed on the next evening, 26 April, although it is disputed whether the second performance was conducted by Toscanini or by Ettore Panizza.
Title: Giacomo Puccini
Content:  Puccini completed La fanciulla del West, based on a play by David Belasco, in 1910. This was commissioned by, and first performed at, the Metropolitan Opera in New York on 10 December 1910 with Met stars Enrico Caruso and Emmy Destinn for whom Puccini created the leading roles of Dick Johnson and Minnie. Toscanini, then the musical director of the Met, conducted. This was the first world premiere of an opera at the Met. The premiere was a great success. However, the compositional style employed in the opera, with few stand-alone arias, was criticized at the time. Some contemporaries also criticized the opera for failing to achieve an "American" tone. However, the opera has been acclaimed for its incorporation of advanced harmonic language and rhythmic complexity into the Italian operatic form. In addition, one aria from the opera, Ch'ella mi creda, has become a staple of compilation albums by operatic tenors. It is said that during World War I, Italian soldiers sang this aria to maintain their spirits. }} The 2008 Italian film, Puccini e la fanciulla (Puccini and the Girl), is based on the period of his life when he was composing the opera.
Title: Tosca
Content:  Tosca is an opera in three acts by Giacomo Puccini to an Italian libretto by Luigi Illica and Giuseppe Giacosa. It premiered at the Teatro Costanzi in Rome on 14 January 1900. The work, based on Victorien Sardou's 1887 French-language dramatic play, La Tosca, is a melodramatic piece set in Rome in June 1800, with the Kingdom of Naples's control of Rome threatened by Napoleon's invasion of Italy. It contains depictions of torture, murder, and suicide, as well as some of Puccini's best-known lyrical arias. Puccini saw Sardou's play when it was touring Italy in 1889 and, after some vacillation, obtained the rights to turn the work into an opera in 1895. Turning the wordy French play into a succinct Italian opera took four years, during which the composer repeatedly argued with his librettists and publisher. Tosca premiered at a time 
Title: Giacomo Puccini
Content:  In 1918, Il trittico premiered in New York. This work is composed of three one-act operas, each concerning the concealment of a death: a horrific episode (Il tabarro) in the style of the Parisian Grand Guignol, a sentimental tragedy (Suor Angelica), and a comedy (Gianni Schicchi).
Title: Giacomo Puccini
Content:  premiered at the Metropolitan Opera, 10 December 1910) ; La rondine, libretto by Giuseppe Adami (in three acts – premiered at the Opéra de Monte-Carlo, 27 March 1917) ; Il trittico (premiered at the Metropolitan Opera, 14 December 1918) ; Il tabarro, libretto by Giuseppe Adami ; Suor Angelica, libretto by Giovacchino Forzano ; Gianni Schicchi, libretto by Giovacchino Forzano ; Turandot, libretto by Renato Simoni and Giuseppe Adami (in three acts – incomplete at the time of Puccini's death, completed by Franco Alfano: premiered at La Scala, 25 April 1926) Puccini wrote orchestral pieces, sacred music, chamber music, solo music for piano and organ and songs for voice and piano, most notably his 1880 mass Messa di gloria, his Preludio Sinfonico of 1882, and his 1890 string quartet movement Crisantemi. However, he is primarily known for his operas:

Question: three act puccini opera first performed in 1900?
Answer: Tosca.