New Orleans Mayor Ray Nagin is to face challenger Mitch Landrieu in a run-off after a mayoral poll considered crucial to the hurricane-hit city's future.
Ray Nagin (left) had a comfortable lead over Mitch Landrieu
Mr Nagin, criticised by some for his response to Hurricane Katrina last August, got 38% in the first round against Mr Landrieu's 29%.
The poll was dogged by race issues as many of the majority black community are still evacuees.
Mr Nagin caused controversy, saying he wanted the city to remain "chocolate".
Mr Landrieu, the lieutenant governor of Louisiana, is the son of the city's last white mayor.
Whoever wins, faces the task of overseeing the reconstruction of a city still struggling to recover from last year's hurricane.
A federal judge refused to postpone the first round, despite fears too many residents scattered by the disaster would be unable to vote.
The vote goes to a second round because no one managed to win 50% of the ballots.
After the results were tallied, Mr Nagin responded to critics who had discounted him because of his mistakes during the Katrina crisis and for his outspokenness, reports the Associated Press.
"There have been too many people who said we were dead, too many people who said we were way too divisive.
"There were too many people who said this city should go in a different direction. But the people have said they like the direction," said Mr Nagin.
Mr Landrieu, currently Louisiana's lieutenant governor, said New Orleans had shown it was "one people".
"We will speak with one voice and we will have one future," he said, flanked by his father, ex-Mayor Moon Landrieu.
Ron Forman, chief executive of a non-profit nature institute, was in third place with 17%.
Much of New Orleans still shows hurricane devastation
The votes of tens of thousands of Katrina evacuees scattered across the United States may have been crucial to the result, the BBC's James Coomarasamy reports.
How many made the journey back to their home city to vote is unclear, although 23,000 filled out absentee ballots.
Some civil rights leaders have called the election unfair because of the lack of out-of-state polling centres and the Rev Jess Jackson has promised to challenge the election in court, regardless of the outcome.
"Iraqi-Americans could vote by satellite to Falluja and to Baghdad," he told a news conference.
"New Orleanians could not vote from Mississippi to New Orleans. So people are coming today by bus and by van and the press carries it as a heroic journey. It is an unnecessary and volatile journey."
Mr Nagin's vow to keep New Orleans a "chocolate city" may have cost him the support of some of those white voters who backed him last time round, our correspondent says.