It was the "rank choice" voting that won Mandani the election. After beating Cuomo, it was effectively all over.
Mamdani solidifies NYC mayoral primary win after ranked choice vote count
Zohran Mamdani appeared to easily secure victory in New York City’s Democratic mayoral primary Tuesday, defeating Andrew Cuomo 56 percent to 44 percent after ranked choice voting results were released by the New York City Board of Elections.
Mamdani, the 33-year-old democratic socialist assemblymember, was already all but certain to win the primary after preliminary election night results on June 24 showed him with a 7 point lead over Cuomo, the former governor. Tuesday’s returns put him well over the 50 percent threshold needed to win with only a fraction of ballots left to count.
https://www.politico.com/news/2025/07/01/zohran-mamdani-ranked-choice-results-00435184