“Una Cosa Rara” was so popular in 18th-century Vienna that when it first was performed in 1786, it overshadowed Mozart’s new opera “The Marriage of Figaro.”

Mozart and Vincente Martin y Soler, who composed the music of “Cosa Rara,” were, in a sense, school chums. Both studied privately under Bologna music composition master Giovanni Battista Martini. And the libretto, or story, of “Cosa Rara” was written by Lorenzo Da Ponte, a frequent partner with Mozart.

“Mozart liked 'Cosa Rara' so much that he borrowed a section and used it in 'Don Giovanni',” said Stephen Lord, Opera Theatre music director. While opera buffs may be surprised to know the banquet scene in “Don Giovanni” is not a Mozart original, that music is actually one of the shimmering melodies from “Cosa Rara.”

Passionate Mozart lovers will enjoy this opera, said Lord, who added that the initial popularity of the opera was easy to explain. Martin y Soler wrote more than 20 operas, which were performed by Europe’s best singers and orchestras. He also gave Vienna something that added to the city's renown. “Una Cosa Rara” is credited with introducing the waltz to the city where it still reigns.

Martin y Soler’s work is familiar to many OTSL regulars. The elegant production of his “Tree of Chastity,” given its American premiere here in 1978, was a hit.

“Una Cosa Rara” was more popular than Mozart’s “Figaro” and “Cosi fan tutte” because its lovely music is less complex and easier to sing, said Corrado Rovaris, the new production’s Italian-born conductor. Rovaris does double duty in the production conducting from the harpsichord.

Neither he nor the opera’s director, St. Louis native Chas Rader-Shieber, expects the new production to make Martin y Soler trendy again. However, for music lovers especially Mozart lovers, this opera puts Mozart’s music in the context of its time, Rovaris said June 2 at OTSL’s “Spotlight on Opera” panel session about the production. OTSL has presented 18 productions of Mozart operas since its first season in 1976.

The story turns on a “rare thing” the “Cosa Rara” of the title -- the faithfulness of a chaste shepherdess. She spurns the love of a prince, a member of a royal family that is particularly wacky, stage director Chas Rader-Shieber said. Keith Phares is the hero Lubino; Alek Shrader is his rival, the prince. Mary Wilson is the Spanish Queen and Maureen McKay is Lilla.

“It’s not a bad libretto and good enough to give it a try today,” said Lord. One of the reasons the opera is rarely produced today is its length. The company got to work and tightened it. “We gave its four acts a trim and now it has two acts in about three hours,” he said. We didn’t hatchet it, we just carefully removed some parts.”

Modern audiences sometimes can miss some of a centuries-old comedy’s humor because of a reverence they give to the stiffness of historic costumes. Stage director Rader-Shieber, set designer David Zinn and costume designer Clint Ramos won’t let that happen to “Cosa Rara.” What Rader-Shieber calls the opera’s “silliness” that captivated the Viennese 222 years ago is underlined with a scattering of comic anachronisms including mute pink flamingos -- instead of peacocks -- on the lawn, a gramophone and costume twists.

Rader-Shieber, a St. Louis native who fell in love with opera at OTSL at 12 when he received opera tickets for his birthday, taught in New York at Juilliard School’s vocal department, and eventually worked his way to OTSL’s backstage as an assistant director in the ‘90s. Now, he’s staged operas throughout the country. He and Zinn have teamed up on “about 40 operas” he said. Last year, the pair made its OTSL directing and set design debuts in “I puritani.” He knows St. Louis audiences and the international set who descend on OTSL for its festival season, so he promised a couple of hundred opera-goers at the “Spotlight” session that they will leave “Una Cosa Rara” smiling.

“Cosa Rara” will have its American professional company debut at Opera Theatre of St. Louis June 8. (The Sunday curtain is at 7 p.m.) The opera is the third production in the company’s festival season. Just five performances will be given in rotation concluding June 20. The work, by a Spanish composer, written in Italian, will be sung in English, as are all OTSL productions.