On the opening night, disaster struck her replacement, the pencil-thin Anne Schwanewilms, at the end of her second big solo, the climactic soaring phrase of Es gibt ein Reich (There is a land), the heroine’s ecstatic outpouring of Todessehnsucht (yearning for death). In Strauss’s original, she has been abandoned on Naxos by the faithless Theseus; in Loy’s production, she is a rich Viennese matron, deserted by her husband or lover, who keeps a page boy, dressed like a little Mozart, in her trunk — these Germans, what are they like? Not only did Schwanewilms fail to reach her high note, she subsequently went to pieces, attempting to drop an octave and mangling her succeeding phrase. Not that many noticed, and she was rapturously received by the audience at the close. She may, of course, have been nervous, as the Royal Opera apparently received letters from Voigt fans menacing a demonstration against Schwanewilms; and she wasn’t really helped by Colin Davis’s broad, loving tempi — for the robust Voigt, these would have been a doddle.

Even without her accident, Schwanewilms is an uncompelling singer — wan of tone, opaque of diction when the orchestra gets Wagnerian — and she presents a droopy figure of maudlin self-pity on stage. I’m sorry, but I don’t get it. Rather the buxom but vocally secure Voigt than this pallid, out-of-tune wraith. Better still, can we please have a proper star — Katerina Dalayman, Nina Stemme or Karita Mattila — next time round? Inevitably, Schwanewilms was outshone by the other ladies on stage, and what ladies they were: Susan Graham, last seen here as Rosenkavalier four years ago, sang the Composer quite gloriously in the all-too-brief prologue, while the young German soprano Diana Damrau was simply the sexiest and funniest Zerbinetta I have ever seen and nearly the most staggeringly well sung. Graham should be an annual visitor to Covent Garden, as she is one of the great American singers of our day, her Strauss trouser roles unequalled.

She pours out her heart, her soul and a stream of gorgeous sound as the palpitating youth whose visionary artistic spirit is compromised by the whims of patrons and the practicalities of opera production. Damrau is certainly the most dazzling star to have emerged from Germany in recent years — according to my companion, she looks like Jerry Hall — and she lights up the stage whenever she appears. Zerbinetta’s high-wire vocal acrobatics hold no terrors for this fearless young woman. Tickets have not exactly been flying out of the box office, but those for the last three performances this week should be snapped up for these fabulous performances alone.

Davis’s conducting of the piece is the antithesis of Antonio Pappano’s: a benign, wise, Karl Böhm-style interpretation, a little short on sparkle for my taste, though the orchestra plays beautifully for him. Covent Garden shoots itself in the foot with its casting of Bacchu: the reliable but portly Richard Margison. Apparently, a tenor can be overweight, but not a soprano. The opera house stands judged of misogyny rather than fattism.

At the Paris Opéra, another glamorous American is bringing down the curtain on Hugues Gall’s distinguished regime in another Strauss work about the “problem” of putting on opera: the valedictory “conversation piece” Capriccio. According to a flyer advertising her previous Paris impersonations of Dvorak’s Rusalka and Massenet’s Manon on DVD, Renée Fleming is an “admirable soprano” and a “Weltstar”, but she is a less than entirely convincing Countess Madeleine in this thesis on the relationship between words and music in opera.

As the muse of the composer, Flamand (Rainer Trost), and the poet (Gerald Finley), Fleming looks gorgeous in Robert Carsen’s grand modern-dress staging (which takes place backstage at the Palais Garnier, the old Paris Opéra, in tribute to Gall). Her creamy lyric soprano is in peak condition, gleaming like a sunburst through clouds as Strauss asks his soprano to soar through the stratosphere. Whatever language she was singing, however, it wasn’t one that I recognise as German — Renée-Flemish, perhaps? — and that, even in these days when people go to the opera to read the surtitles, is a fatal flaw in this of all operas.

With Anne Sofie von Otter, almost unrecognisable as a hilariously “actressy” Clairon, the diva of the Comédie-Française, and Franz Hawlata, got up to resemble Gall, as the impresario La Roche, the star of this Straussian show, as in London, is outshone by the support. Gall had evidently planned this as a luxury goodbye present to himself: Dietrich Henschel is the Countess’s randy brother, while among the cameo roles, Britain’s Barry Banks shines as a wickedly funny parody of Italian tenorial vanity, and the ageless Robert Tear touches the heart as the dozy prompter, M Taupe. Christian Thielemann, one of the world’s deluxe Straussians, should have conducted, but he is acquiring a reputation as a canceller and was replaced at the early performances by the solid Günter Neuhold, and by Ulf Schirmer, who recorded this opera with Kiri te Kanawa, for the remaining ones.

Capriccio and Ariadne are companion pieces, fascinating to see in tandem, but you’ll be lucky to get a ticket for the Palais Garnier. They are cheaper than Covent Garden’s, of course — subsidy, subsidy — but this is a tale of two cities, in which Paris still outflanks London. Top-quality opera is hugely popular in the French capital, which has five busy houses, without the need for stunts such as La bohème in Trafalgar Square.