It was Saturday night, and the crowd inside a Manhattan concert venue was getting primed. A D.J. was stationed in the front, a brass band held the rear, and celebrity guest stars waited offstage alongside the main attraction, Zohran Mamdani.

Hours earlier, an older, smaller but enthusiastic audience clapped their hands to gospel music and greeted Andrew M. Cuomo in Harlem at the headquarters of the Rev. Al Sharpton’s National Action Network.

The two events, held as New Yorkers flocked to the polls on the first day of early voting in the New York City mayor’s race, had the same objective, with the two leading candidates surrounding themselves with prominent allies and reinforcing the core themes of their campaigns.

But they looked and felt very different, underscoring their contrasting messages and the generational divide of the candidates and their supporters.

The Kid Mero, the comedian and podcaster, played the emcee at Mr. Mamdani’s rally at Terminal 5, a venue on Manhattan’s Far West Side. Representative Alexandria Ocasio-Cortez delivered the introduction, arguing that Mr. Mamdani was the kind of leader that Democrats should be embracing across the nation.

Ms. Ocasio-Cortez, who endorsed Mr. Mamdani as her first choice in the race, said she was disappointed by Democrats who called on Mr. Cuomo to resign in 2021 after a sexual harassment scandal, yet now support him for mayor. She said that Mr. Cuomo was part of a troubling “gerontocracy” in politics and that the city could not become a city only for the rich.