From left, Antonio Figueroa, Pascale Beaudin, Jeffrey Thompson, Claire Debono, Blandine Staskiewicz and Alex Dobson in Opera Lafayette's production of Les Femmes Vengées by Philidor at the Kennedy Center. (Louis Forget)

Opera Lafayette has twice defied expectations with its “Cosi project” double bill.

When they performed Mozart’s famous “Cosi fan tutte” in French in October, with the recitative cut and offered as spoken dialogue, with a new silent character written in, and an orchestra with little experience of playing the piece, you might have expected it to be awful. Instead, the production was delightful.

On Thursday and Friday night, they followed up with “Les femmes vengées,” an opera by François André-Danican Philidor that was wildly popular in the 18th century and basically forgotten since. This is the kind of thing that Opera Lafayette usually hits out of the park. Yet, on Friday at least, the evening proved a fragile soap bubble that burst early under the compound weight of anodyne music and too much French dialogue delivered in heightened, stylized tones.

In other words: They got the harder and more important piece right.

The two operas are going to be presented as a double bill in New York on Thursday and in Versailles, France, the following week. Washington didn’t get the full weight of the comparison, alas — or fortunately.

Putting the two operas together was a provocative idea: They share similar plot outlines (two couples setting out to test each other’s love), and Mozart may well have seen Philidor’s opera while he was in Paris in 1778. But Ryan Brown, Opera Lafayette’s founder and music director, a specialist in French opera, conceded beforehand that Philidor — whose “Sancho Panca” the company presented in 2010 — couldn’t hold a candle to Mozart, suggesting that “Les femmes vengées” was a wonderful dessert after the main course of “Cosi.”

I didn’t get to see the double bill, but I can say that two iterations of similarly frothy plots — in “Les femmes vengées,” the wives learn that their husbands are making a play for another woman, and teach them a lesson by pretending to be in love with that woman’s husband — is rather a lot of a good thing. And the musical expression in the Philidor consisted mainly of long, repetitive arias, which sounded thin against even the implicit comparison to Mozart, and did little to elevate the characters above broad caricature.

Opera Lafayette’s conceit, carried out by the director Nick Olcott, is that the operas involve the same characters, with “Les femmes vengées” set 10 years later: The couples are married off (in the pairings they had at the end of “Cosi,” rather than going back to their original partners) and the men have become provincial country dignitaries. Delphine (Despina in Mozart’s original), now the object of their desire, is happily married to a painter, M. Riss, the silent character in “Cosi,” who now finally got to find his voice. (Jeffrey Thompson, in the role, demonstrated a soft, light meringue-y tenor voice that was sometimes pretty and sometimes inaudible.)

But Olcott couldn’t help the singers speak fully convincingly — a task made all the more difficult by the fact that most of the dialogue is playacting as the wives enact a charade of love to dupe, and chastise, their listening husbands. Add to this the generally unexciting music, and the singers, who won me over in “Cosi,” had little chance to shine. Antonio Figueroa, as Ferrand — now “M. le Président” — had gained in assurance, but none of the women — Blandine Staskiewicz as Dorabelle/Madame Lek, Pascale Beaudin as Fleurdelise/Mme. la Président, or Claire Debono as Delphine — got to do much more than coquette. Like Alex Dobson as Guillaume, their singing was adequate, but not impressive, though Brown and the orchestra made of the score what they could.

I actually found it far more illuminating to see “Cosi” in French than I did to see this juxtaposition, which suffered further from the fact that the Philidor, performed after “Cosi,” was written before it, so sounded all the more stylized in comparison. I think it might take an ensemble of actors from the Comedie Française to bring “Les femmes vengées” to life.

Still, the novelty of the project, and of the comparison, will make the double bill worth seeing. And to say that the Philidor is by far the lesser work is only to state the obvious. In the final ensemble, the characters sing that it’s best not to look too closely at details if you want to have a happy life, and M. Riss makes an open appeal to the audience to apply the same principle to judgment of this opera — one of the evening’s most charming moments, because it’s one of its most telling.

The double bill will be performed at Lincoln Center’s Rose Theater in New York on Thursday, and at Versailles’s Opera Royal on Feb. 1 and 2.