The runoff will be held Dec. 1. Unofficial results show veteran city councilwoman Mary Norwood is earning the most support with 45 percent. She is seeking to become the city's first white mayor in nearly four decades.
State Sen. Kasim Reed, who is black, is in second place with 38 percent with 100 percent of precincts reporting and with early voting totals.
One candidate needs to get 50 percent of the vote plus one.
City council President Lisa Borders was trailing in third and conceded about three hours after polls closed Tuesday.
Current Mayor Shirley Franklin, the city's first female mayor, was barred from seeking a third term.