Tristan und Isolde is a fiendishly difficult opera to produce. The requirements on the singers are immense. Keeping the integrity of a single musical argument which spans four hours is an opera conductor’s challenge of the highest order. And you are expected to stage short grand opera crowd scenes amidst a work which, for most of its duration, is a chamber opera: a battle of ideas fought in duets. But if all these problems can be overcome, as they were at Covent Garden last night, the result is a masterpiece.

Wagner himself doubted that he would ever find singers capable of the title roles. It’s the sheer stamina that is terrifying: in Act II, for example, Isolde is singing nearly continuously for the majority of the 80 minutes. He would surely have been happy with the pairing of Nina Stemme and Stephen Gould.

In Act I, Isolde is angry with a capital A. Some sopranos conserve energy in preparation for the ordeal to come: Stemme did not. She threw herself into the role from the first notes, able to bring both fury and faltering regal dignity. Her voice has power without ever going harsh at the top, her diction excellent (which is critical for such a wordy opera) and she has a great deal of control over her timbre, allowing her to portray the dramatic changes in Isolde’s character as the opera progresses: fury and then coy slyness with Tristan in Act I, wilful headstrongness followed by sweetness and rapture in Act II, despair in Act III.

The role of Tristan needs its stamina in Act III, and Stephen Gould was also well up to the task. His voice has marvellous mellowness in its upper register, with the uncanny trick of the notes sounding progressively less forced the more he approaches a big high note - the exact opposite of what you might expect. When the music turns to rapture, he provides wonderful sweeping phrases. The control wasn’t quite there in some of the softest pianissimi, but this was a voice I could have listened to all night.

The secondary roles received the Royal Opera’s usual treatment of revivals: flood them with big names. As Brangäne, Sarah Connolly was solid and reliable rather than outstanding – rather like her character – but still produced one of the outstanding vocal moments of the evening, the “Einsam wachend” in which she urges the lovers to think of her as she watches over them. Iain Paterson was a first class Kurwenal, bringing to life the bizarre mixture of coarseness, warmth and nobility that he embodies in Act III. John Tomlinson no longer sustains the length of phrases of the past and it sometimes sounds as if he is reaching for notes, but when the notes are reached, they remain undimmed: the voice is loud, resonant and smooth. He made us feel utter sympathy for King Marke: a powerful man who strains every ounce of his being to bring goodness and reconciliation, but in the end is left utterly bereft.

With the help of a long interview in the programme notes, Christof Loy’s modern dress staging makes a lot of sense. Loy zeroes in on the central philosophical premise of the opera – the battle between “Night” (the realm of passion in which Tristan and Isolde are immersed) and “Day” (the forces of external reality in which they must still function). The stage is split lengthways by a curtain: in the front, we have Night, where the stage is virtually empty and we only have the protagonists’ discourse on which to focus; behind it and only glimpsed occasionally is Day, where there is light, glitter and feasting. The setting is spartan, but it works well: when we are listening to one of the many duets in the opera, we can focus completely on the characters and acting – and Loy extracted credible acting performances from all his singers.

Musically, the problem of Tristan und Isolde can be simply put: here is an opera in which the emotional temperature is steadily raised in a musical architecture which highly unified from beginning to end. However, the orchestra cannot possibly play a single four hour crescendo. So the conductor must weave some magic in controlling the ebb and flow of the music so that each climax feels more intense than the last. Last night, Pappano was magnificent. The harmonic integrity of the work was clear to our ears; the passionate swell came through superbly and there was an obsessive level of attention to detail in individual instrumental sound: I will particularly remember the growling double basses in the prelude to Act III.

This production may have had its imperfections (there was the odd cracked note, and I suspect, for example, that if you were high on the far left of the audience, you may have missed a lot of the action). But with such an outstanding orchestral performance, superb singers who sang flat out for the whole evening, and a staging that allowed us to focus on the psychology of each character at each moment, this Tristan und Isolde is one to savour.