In a 2009 interview, Plácido Domingo said that he could not imagine retiring from opera with a series of farewell performances and public celebrations. The time to stop will just come to him when it’s right, he explained.

“I think it will be one evening,” he said, “after a performance, to say, ‘That’s it.’ ”

It may be the moment for Mr. Domingo to heed his own words. On Friday night, Mr. Domingo, 74, among the most gloried tenors of all time, seemingly determined to keep his career going, sang another baritone role: Don Carlo, the king of Spain, in the Metropolitan Opera’s revival of Verdi’s “Ernani,” an early work. It’s not hard to understand one reason Mr. Domingo finds it impossible to retire from the stage: He still has devoted fans. On Friday he drew bravos for his arias. During curtain calls, as Mr. Domingo bowed and waved, a sea of mobile phones in the house captured the moment on video.

But his voice is now quite compromised and his performance showed it. He pulled off the role. There were flashes of the Domingo vocal charisma we remember from his decades of magnificent singing. But he seemed to be pushing his voice and sometimes barked lines, especially stretches of dramatic recitative. He also tended to cut off the ends of phrases, as if giving the vocal line one final push. Despite traces of the dark Domingo colorings, richness and power, his voice mostly sounded leathery. I missed a hallmark of Mr. Domingo’s glory days: smooth, legato phrasing.

He often seemed preoccupied with the technique of singing, so much so that his performance could be musically careless. During solo flights, he sometimes rushed a line and other times became bogged down dispatching an embellishment, resulting in his veering off track from the orchestra, even with James Levine, a conductor who can follow anyone, in the pit. Mr. Domingo is one of the most comprehensively skilled musicians in the field of opera. Does it not bother him to be fudging?