This sensuality of course presages where the plot is going it peaked in the Act two love duet, which, even more than the Prelude, was a dream of orchestral and vocal beauty. In that second bar, the famous “Tristan chord”-which opened a new harmonic world for music-lovers at the opera’s 1865 premiere, and which Wagner carefully orchestrated for maximum bite, with double reeds high in the mix-didn’t sting, it bloomed and the entire Prelude unfolded, at De Souza’s expansive tempo, in curvaceous, soft-edged lines, languid, even erotic. It turned out to be special in several ways, in fact. 29) would be sonically something special. From the second bar of Richard Wagner’s “ Tristan und Isolde,” in the hands of conductor Jordan De Souza, it was clear Seattle Opera’s production (which opened Saturday night and runs through Oct.