Lt. Gov. Mitch Landrieu, who lost to Nagin in a runoff four years ago, was widely seen as the front-runner in an 11-candidate field. Were he to win an outright majority, he would become the majority black city's first white mayor since his father, Moon Landrieu, left the post in 1979. But other candidates, vying for second place, were hoping to deny him a majority and force a March 6 runoff.
Among them was businessman John Georges, also white, who has pumped $3.4 million of his own money into his campaign. Polls have also shown business consultant Troy Henry, an African-American making his first political run, as a contender.
Attorney Rob Couhig, housing consultant James Perry and former Judge Nadine Ramsey rounded out the field of better-known candidates.
Nagin was barred from seeking re-election under a term limits law.
Continued violent crime, city budget problems and an uneven recovery from Hurricane Katrina, which devastated the city in 2005, were among the issues.
But residents could be distracted because they are caught up in excitement over the New Orleans Saints' first appearance in pro football's Super Bowl championship game on Sunday and preparations for the start of Carnival season.
Secretary of State Jay Dardenne projected turnout as high as 45 percent in a city where registered voters number more than 273,000.
More than 16,000 people cast early votes earlier this month.