When sopranos have moved down to mezzo-soprano and contralto roles late in their careers, as Régine Crespin (Mère Croissy in "Dialogues des Carmélites," Madame Flora in "The Medium"), Astrid Varnay (Widow Begbick in "Mahagonny," Herodias in "Salome") and Leonie Rysanek (Klytämnestra in "Elektra," the Old Countess in "Queen of Spades") did, the transitions have generally not been jarring. While tenors and baritones alike sing Pelléas and, in operetta, Eisenstein ("Fledermaus") and Danilo ("Merry Widow"), the divisions between higher and lower male voice categories are usually more rigid. Having tenor Plácido Domingo blur the lines and assume a dramatic baritone part, the title role in Giuseppe Verdi's "Simon Boccanegra" (1857, revised 1881), takes some adjusting to-which is not to say that he hasn't prepared us, playing Marcello to Luciano Pavarotti's Rodolfo, in the duet "O Mimì, tu più non torni," from Act Four of "La Bohème" in a Metropolitan Opera gala; singing in a baritone register in the title role of Tan Dun's "The First Emperor," written for him, and as Oreste in Christoph Willibald Gluck's "Iphigénie en Tauride," both with Paul Groves as the tenor in his life; and doing the "Boccanegra" duet, "Orfanella il tetto umile," with Angela Gheorghiu in the Met's 125th anniversary gala. But never has Domingo's baritonal tenor sounded more tenor-y than in his full performance as the baritone pirate-turned-Doge of Genoa in "Boccangra," which returned to the Met repertory on January 18. The third of six performances, on January 25, is considered here.

Domingo undeniably boasts the gravitas and stature to play this role and brings the expected full intensity to such significant moments as finding his beloved Maria (senior) dead and being named Doge in quick succession, in the prologue, and pronouncing a vehement curse upon the abductor of Maria (junior), at the end of Act One. Such high, lyric moments as the quiet exclamation of "Figlia!" (daughter), starting on high F, near the end of Act One, Scene One, and the soaring lines "E vo gridando pace!/E vo gridando amor!" (I cry for peace, I cry for love), in the aria "Plebe! Patrizi!" in Act One, Scene Two, challenges for a baritone, were almost too easy for Domingo, which scarcely means that he gave the low phrases, preceding the curse, anything less than their due. But every time a high tenor phrase rang out, one had to remind oneself that it was Marcello Giordani, as Gabriele Adorno, singing, and not Domingo, for when both appeared on stage together, there was little contrast between their voices. All that said, Domingo's effort was never less than one of full artistry and commitment-just that it was different. It may be that, while he feels quite ready to turn to Boccanegra, it's we, the audience, who are obliged to catch up to him.

Adrianne Pieczonka, who portrayed Amelia Grimaldi, who turns out to be Maria Boccanegra, the Doge's daughter, and who came out publicly in a recent Opera News magazine interview, lent a tangy and radiant spinto soprano to "Come in quest'ora bruna," her entrance aria; to her narrative, describing her abduction; and to her parts in the grand concertato following "Plebe! Patrizi!" and other numbers. Pieczonka went from an impassioned duet with Giordani, as her tenor lover, to a tender one with Domingo, as her tenor father, and back again. Giordani offered a formidable account of "E il furor che m'accende," the furious recitative, and "Cielo, pietoso, rendila," the romanza, music sung by Domingo himself not so long ago.

James Morris, as Jacopo Fiesco, the first Maria's father and Simone's archenemy, delivered a sonorous "Il lacerato spirito," mourning his daughter, and had aptly fraught confrontations with Domingo at the beginning and end of the opera, but sounded underpowered on climactic low notes at the ends of the aria, the first duet, and the announcement of Simone's death. As Boccanegra's other foes, not such fully fleshed-out figures, Patrick Carfizzi, as Paolo Albiani, and Richard Bernstein, as Pietro, gave solid performances, save for a raucous top note from Carfizzi early in Act Two. Joyce El-Khoury and Adam Laurence Herskowitz completed the cast.

Maestro James Levine, presiding over the Met Orchestra, proved, unsurprisingly, in full command of the dynamic range demanded by the score, from the saber rattling, thunder and intrigue of many of the scenes to the delicate tonal painting, depicting the sea, at the start of Act One. The Chorus made strong showings calling for "Vendetta," in the towering Council Chamber scene, and rebelling ("All'armi, all'armi, o Liguri!"), at the end of Act Two.

Further performances of "Simon Boccanegra" take place on January 29 and February 2 at 8 p.m. and February 6 at 1 p.m. J. David Jackson conducts on January 29 and Nicola Alaimo (debut) plays Paolo at the repetitions remaining. For tickets, priced from $15 to 375, telephone 212/362-6000, visit www.metopera.org, or go the Met box office at Lincoln Center. Rush tickets, for $20, will be available at the box office, on the day of performance, for the February 2 hearing.