“I know. Let’s record all 70 Donizetti operas. Including the ones where the scores are in bits in some library somewhere.” It’s the kind of conversation that sounds great in the pub but is swiftly forgotten the morning after. But Opera Rara are made of sterner stuff. Their latest Donizetti excavation, L’Ange de Nisida, should have been an important opera for the composer’s burgeoning Paris career, but the bankruptcy of its promoter in 1840 led to its demise and dismemberment (literally: parts of the autograph score were ripped out and reused for La Favorite). It's taken a decade of work by Candida Mantica to reconstruct a playable score, which last night gave Opera Rara the honour of playing a world première of a Donizetti opera at Covent Garden.

L’Ange de Nisida is an example of a genre we hardly ever see now: the opera semiseria, a dramatic opera usually distinguished by the presence of a basso buffo – in this case, the King’s chamberlain, Don Gaspar. Far from providing mere comic relief, he is the comic pivot around which the tragedy revolves, a Boris Johnson character, a self-satisfied, egotistical buffoon whose bloated self-importance is immune to understanding the consequences of his antics. Laurent Naouri plays Gaspar to perfection, as well as being vocally strong: it takes a lot to survive singing buffo patter at the base of a quintet where the other singers are in full Donizettian lyric flood.

The plot is artfully constructed. Sylvia, our heroine, is the mistress of Ferdinand, King of Naples. He worships her, she puts up with him. Our tenor hero Leone falls in love with Sylvia; she is attracted but brushes him off; meanwhile, trouble is arriving in the shape of a monk sent by the Pope to instruct Ferdinand to discard Sylvia (we’re in 1470, and the Pope is terrified that she will entrap Ferdinand into a politically unsuitable marriage). Each of our characters is unaware of key information about the others, and Gaspar’s “cunning plans” to resolve the situation lead to disaster.

As the Monk, Evgeny Stavinsky gave us a bass performance to savour: his voice is youthful, virile and full of warmth and depth, one of those voices that make you sit up from the very first notes. This is his first performance at Covent Garden, and I hope there will be many more to come. Ferdinand is a shallower role – the main task is to be infatuated with Sylvia and angry with everyone else – but Vito Priante sang credibly.

L’Ange de Nisida was written at the point in opera history where tenor roles were in transit from light and lyrical to heavier and more dramatic. David Junghoon Kim’s Leone was more lyric than dramatic: it’s a clear voice with a lovely turn of phrase, but in the first half, it felt a size too small for the role. After the interval, however, as the action darkened, Kim’s voice darkened with it, and he was particularly persuasive in the highly dramatic dénouement when Gaspar’s trickery has been revealed and Leone furiously breaks his sword and throws the shards at the King’s feet.

Joyce El-Khoury did not begin the evening at her best, tentative in pianissimi and not quite bringing her voice to full bloom in all registers. But she also seemed inspired by the darkening mood of the music as the story unfolded and her last act was deeply affecting (it’s probably not too much of a spoiler to inform you that the soprano dies tunefully at the end).

Emerging from the safety of their pit but sheltered under a protective forest of microphones, the Royal Opera Orchestra performed with excellence. While some of Donizetti's orchestration is vulnerable to the “big guitar” jibe, a great deal of it is more interesting, with varied use of winds and pizzicato effects. Sir Mark Elder showed all of his experience in achieving immaculate balance with the singers – something we’ve often seen go wrong when the orchestra is playing through them in a concert performance – and brought out plenty of orchestral colours while keeping everything moving forward. The chorus sang well, urgent and audible in spite of singing from the back. Both the chorus and soloists gave us surprisingly good French diction.

L’Ange de Nisida is short of knockout solo arias: the strongest numbers range from duet to quintet. But it’s a beautifully constructed piece which made for a thoroughly enjoyable evening, as well as being a real advertisement for the little-known genre of opera semiseria. Let's hope someone stages it soon.