With all the precincts and absentee ballots reported in Saturday's nonpartisan primary, Nagin topped all candidates with 38 percent or 41,489 votes but fell short of the majority he would have needed to win a second term and avoid the May 20 runoff.
Landrieu had 29 percent, or 31,499 votes. Nonprofit executive Ron Forman followed with 17 percent, 18,734 votes, and 19 other candidates trailed far behind.
In his late-night speech at his election headquarters, the glib Nagin took a jab at his critics who had counted him out because of his missteps during the Katrina crisis and for an outspokenness some saw as divisive.
"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," Nagin said.
"We'll no longer be a city of haves and have-nots," he said. "This economic pie that is getting ready to explode before our eyes is going to be shared equally."
Landrieu struck a similar theme, saying his showing was testament to the unity the city needs after a storm that put all of New Orleans "literally in the same boat."
"Today in this great American city, African-American and white, Hispanic and Vietnamese, almost in equal measure, came forward to propel this campaign forward and loudly proclaim that we in New Orleans will be one people. We will speak with one voice and we will have one future," he said, flanked by his father, Moon Landrieu, the last white mayor of New Orleans.
Elections officials say the voting was steady and unusually problem-free. The turnout was low, roughly a third of those eligible.
Of the city's 297,000 registered voters, tens of thousands are spread out across the United States. More than 20,000 cast ballots early by mail, fax or at satellite voting stations around the state, and thousands more made their way to 76 improvised polling stations. Some traveled by bus or in car caravans from such evacuee havens as Houston, Dallas and Atlanta.
Vera McFadden came all the way from Texas just to vote. "I vote for every, every election. I don't care what it is. I don't miss voting. And my voice I want to be heard," she told CBS News correspondent Mark Strassmann.
McFadden's home since 1951 now sits ruined in her backyard, Strassmann reports. It's located in the Lower Ninth Ward, which may not be rebuilt. McFadden wants to rebuild her home — and her city's future. And that's what this election is all about.
"I wanted somebody that's going to be able help serve this city," she said, "for all communities."
"Let me tell you something. This is an important election," said Gerald Miller, a 61-year-old stroke patient whose daughter was pushing her in a wheelchair. "We're going to straighten this mess out."
Around the city, a mixture of black and white voters were seen moving steadily in and out of the "super polling places" that stood for the dozens of wrecked schools and churches where residents would ordinarily have voted.
"It means a lot because whoever gets elected is going to help us rebuild," said 57-year-old Lorraine Payton. "This is about trying to save us right now."
The winner of the mayoral and city council races will face a host of politically sticky and racially charged decisions about where and what to rebuild in a city where whole neighborhoods remain uninhabitable.
Four-fifths of the city was flooded, and large parts of New Orleans are still woeful tracts of ruin. Rebuilding plans - and the federal money to pay for them - are being debated. Nearly all the public schools remain closed, and the tourism business, long the economy's mainstay, has drawn few conventions.
Nagin said at a precinct in his neighborhood Saturday that, with another hurricane season just weeks away, this is no time for a transition of administrations. "We don't have a year to wait," he said.
The 49-year-old former cable television executive became known in the immediate aftermath of Katrina for sometimes shaky leadership and frequent off-the-cuff remarks, such as when he cursed the sluggish federal response and later suggested that God wanted New Orleans to remain a "chocolate" city. Nagin, who is black, later apologized for the chocolate city comment, saying he didn't mean to offend anyone.
Landrieu, brother of Senator Mary Landrieu, has shown the ability to bring in voters across color lines. His father, Moon, was widely noted for bringing blacks into his administration in the 1970s.
Forman, chief executive of the Audubon Nature Institute, which oversees the city's zoo and aquarium, had also been seen as a strong white challenger. He won the endorsement of business leaders and the city's major newspaper, The Times-Picayune. In his concession speech, Forman made no endorsement and pledged to work with whoever wins the runoff.
Race has become a key factor in the election. Less than half the city's pre-Katrina population of 455,000 have returned, and civil rights activists note that most of those scattered outside the city are black. Prior to the storm, the city was more than two-thirds black; it has not had a white mayor since 1978 when Moon Landrieu left office.
Civil rights leader the Rev. Jesse Jackson has said he plans to challenge the election outcome in court regardless of the winner, arguing displaced voters were disenfranchised because they weren't allowed to vote in polling places in such adopted cities as Houston, Dallas and Atlanta.
Of the ballots cast prior to Saturday's election, about two-thirds were cast by black voters, but analysts caution the numbers may not reflect overall turnout. The racial breakdown of the full vote was not immediately released.
Secretary of State Al Ater said he's confident that election officials, who fielded thousands of calls from voters on where to vote, did what they could to educate voters.
But not all evacuees who returned to New Orleans on Saturday were able to cast ballots. Dana Young, an 18-year-old college student who traveled by bus from Atlanta, was told at the polls that there was no record of her registration. Young said she had a voter reg