In a stunning upset, Mayor Bloomberg’s City Council candidate David Greenfield trounced his opponent, Joe Lazar, in a race for the Brooklyn seat tonight.

Greenfield, a longtime political fixture in the Orthodox Jewish community he was elected to represent, secured 58 percent of the vote, to 39.5 percent for Joe Lazar.

Lazar had the backing of Assemblyman Dov Hikind (D-Brooklyn) and the powerful Assembly Speaker Sheldon Silver (D-Manhattan), and had more momentum heading into the special election.

But Greenfield stumped with Bloomberg throughout the Boro Park neighborhood last week and pulled off the defeat, despite his cooling in recent years with Orthodox Jews in Brooklyn.

The seat was held by Simcha Felder, a Democrat, who won reelection last year but resigned to become a deputy comptroller for the newly elected John Liu.