Vlada Borovko is beginning to make a habit of hitting the big stage at Covent Garden when the prima donna gets sick on the night. In La traviata last year, she was a credible Violetta when Maria Agresta withdrew during the afternoon. Last night, Albina Shagimuratova was taken ill just an hour before curtain for Mozart’s Mitridate, re di Ponto, and Borovko stepped into the breach once more for the key role of Aspasia. All things considered, she sang remarkably well, a bright voice with plenty of sheen and the agility required for Mozart’s gymnastic coloratura.

That said, Borovko is a far cry from the combination of sparkle and sheer vocal heft that Shagimuratova can bring to a role. So combined with the earlier withdrawal of Anett Fritsch, that took us from five big stars in the main roles down to three – and that matters to an opera written at the time when the audience’s focus on the vocal talents of its stars was at its highest. In that respect, and in its opera seria nature as a series of recitatives interspersed with da capo arias, Mitridate feels more like very late Handel than early Mozart – he was just 14 when he wrote the opera, and while Mitridate is full of glorious vocal writing, it gives little hint of the transformation to the form that would occur with Mozart’s later works.

In the absence of Fritsch and Shagimuratova, the title of Queen of the Coloratura fell easily into the lap of Lucy Crowe, whose voice is perfectly suited to this music: the clarity is there, the diction is good and when it’s time to navigate the high speed flying up and down the register, Crowe has so much ease, security of pitch and so much in reserve that she can really thrill with her phrasing. Equally thrilling was Michael Spyres in the title role, whose high register uniquely combines brightness and high calibre firepower, exactly what was needed to portray the haughty, arbitrary absolute monarch.

The plot action in Mitridate is relayed by means of extensive recitatives, and much of the opera’s success depends on the ability of the performers to retain our interest during these, keeping the pace from dragging and making us believe in the story through the expressivity of their voices. All of our seven soloists did a fine job of this, helped in no small measure by the virtuosity of Christophe Rousset both as continuo player and conductor – in Rousset’s hands, I never felt that here was “yet another similar recitative”. The most convincing was countertenor Bejun Mehta as Mitridate’s errant son Farnace: Mehta was urgent, nuanced and credible at all points, with his aria “Venga pur, minacci, e frema” one of the highlights of the evening. The opera’s greatest hit, Sifare’s “Lungi da te”, was disappointing, not so much because of Salome Jicia’s singing but because its horn solo – crucial to the effect of the piece – was rather prosaic and far too loud for her voice.

Graham Vick’s 1991 staging is, to say the least, improbable. Paul Brown’s sets are plain and extremely brightly coloured – mainly floor to ceiling poster red with a slight patina, occasionally replaced by royal blue. Props are at a minimum. The extraordinary costumes are in primary colours with lashings of plastic armour for the men and giant hooped skirts – conical in shape for the women, a sort of flattened out farthingale for the men (Shagimuratova's similar farthingale would not have fitted Borovko). The armour and much of the costumery had a sort of Far East feel, except for the distinctly Mozartian wigs.

For the first part of the opera, stage movement and interplay between characters was at a minimum and I had the feeling of being in an elaborately coloured and costumed concert performance. As the evening progressed and Mitridate’s contingent arrived, there was complex choreography: Mitridate’s six attendants were doing something inspired by martial arts, while Lucy Crowe’s Ismene was doing head movements out of Indian classical dance, much hand fluttering, and body moves reminiscent of Olympia the mechanical doll from Les Contes d’Hoffmann. I felt like I had been parachuted into some weird, gender-ambiguous, primary-coloured animé. And I couldn’t work out the acting: Crowe and Mehta appeared to be taking the whole thing with a big dose of knowing irony, while Spyres, Borovko and Licia were playing it perfectly straight.

A strange evening: superb Mozart playing from Rousset, plenty of fine singing, staging and costumes that one certainly isn’t going to forget. But what’s the point of it all? I’m not really sure...