The election results watch party for former Gov. Andrew M. Cuomo got off to a fairly subdued start on Tuesday evening. Guests mingled as music played at a low volume over muted televisions displaying the results, and only a few “Cuomo for Mayor” signs decorated the event space.

As the night progressed and results rolled in, the crowd found no reason to become more energized.

Mr. Cuomo took the stage around 10:20 p.m. and told his supporters that “tonight was Assemblyman Mamdani’s night.” One dismayed supporter shouted that the race was not over yet, a seemingly last-ditch effort to dissuade the former governor from conceding to Assemblyman Zohran Mamdani.

The Cuomo backers had gathered in a cavernous space on the fourth floor of the Carpenters Union Hall in downtown Manhattan. The night’s proceedings were confined to a corner of the hall, with a handful of orange “Carpenters for Cuomo” signs leaning against a white wall.

One only prominent supporter made the rounds among the crowd.

Jessica Ramos, a state senator and mayoral candidate who endorsed Mr. Cuomo, said after she arrived that the former governor’s campaign was “feeling good” about the high voter turnout on Primary Day, especially given the extreme heat. Ms. Ramos said that the election would “define what being a Democrat means.”

Just moments before Mr. Cuomo took the stage, Ms. Ramos remained optimistic.

“The results we’ll see tonight paint a very specific picture that perhaps does not tell the whole story,” she said.

Then, Mr. Cuomo struck a different tone, congratulating Mr. Mamdani on his victory. As he left the stage, stunned supporters headed for the exit.