Former White House chief of staff Rahm Emanuel, just elected mayor of Chicago, called his victory "humbling" and "most gratifying".
He also thanked retiring mayor Richard Daley for his lifetime of service to the city.
Mr Emanuel said he was ready to meet the challenges head-on to "make a great city even greater".
He had already received the congratulations of his former boss, US President Barack Obama.
With 89% of the precincts reporting, Mr Emanuel was trouncing five opponents with 55% of the vote - a margin that let him avoid an April runoff.
It was the city's first mayoral race in more than 60 years without an incumbent on the ballot and the first in more than two decades without Mr Daley among the candidates.