Public Advocate Bill de Blasio, who ran an upstart campaign pledging to fight New York City's economic inequality, emerged as the surprising top choice in the Democratic mayoral primary, but could still face weeks _ and another electoral fight _ before becoming his party's nominee.

The swirling, chaotic campaign to replace billionaire Mayor Michael Bloomberg, which featured former congressman Anthony Weiner's latest sexting scandal and at least three lead changes in the polls, was fittingly plunged into uncertainty again after the votes were tallied in Tuesday's primary.

With 97 percent of precincts reporting, de Blasio had about 40.2 percent of the total vote, which puts him a whisker above the 40 percent threshold needed to avoid triggering an automatic Oct. 1 runoff. If he cannot maintain that, he will face former city Comptroller Bill Thompson, who has 26 percent, for a potentially grueling three-week, one-on-one showdown, with the winner advancing to face Republican nominee Joe Lhota, the former chairman of the Metropolitan Transit Authority, in the general election on Nov. 5.

But it may take a week or more before it is known whether that battle will be fought at all.

The campaign will take a pause Wednesday as the city stops to observe the anniversary of the Sept. 11, 2001, terrorist attacks. Later this week, election officials will recount all the ballots cast Tuesday. It will likely take until early next week before they tabulate an additional 30,000 or more votes as absentee ballots arrive by mail and paperwork comes in from voters who had problems at the polls.

City Council Speaker Christine Quinn, the early front-runner who was seeking to become the city's first woman and openly gay mayor, finished third at 16 percent, followed by current city Comptroller John Liu at 7 percent and Weiner at 5 percent.

De Blasio, who was flanked by the interracial family he made a centerpiece of his campaign ads, made no mention of the potential runoff in his speech to supporters late Tuesday.

"We are better as a city when we make sure that everyone has a shot," de Blasio told the raucous crowd. "We begin tonight."

The winner of the mayor's race in November will assume the helm of the nation's largest city which has been led for 12 years by Bloomberg. The election comes at a critical juncture as the city experiences shrinking crime rates yet widening income inequality, and as the nearly completed One World Trade Center building symbolizes a new era after the terrorist attacks of 2001.

With de Blasio so close to 40 percent, Democratic leaders may pressure Thompson to drop out of the race in the name of party unity. Exit polling shows that de Blasio would handily defeat Thompson in a runoff, 52 to 34 percent, with 9 percent saying they would stay home.

But Thompson made it clear Tuesday he would compete in a potential runoff.

"Three more weeks! Three more weeks!" chanted Thompson, the party's 2009 nominee. "This is far from over."

De Blasio's rise in the race to succeed Bloomberg was as sudden as it was unexpected.

Not even two months ago, he was an afterthought in the campaign but surged in part thanks to an ad blitz that centered on his interracial family, his headline-grabbing arrest while protesting the possible closure of a Brooklyn hospital and the defection of Weiner's former supporters in the wake of another sexting scandal.

Weiner was leading in the polls until a gossip website revealed that he used the online handle Carlos Danger to continue to send X-rated messages to women even after he resigned from the House of Representatives in 2011 for similar behavior.

The exit polling showed the appeal of de Blasio, the city's elected public advocate, to be broad-based: He was ahead in all five boroughs; was ahead of Quinn, the lone woman in the race, with female voters; and ahead of Thompson, the only African-American candidate, with black voters. The voter interviews were conducted by Edison Media Research for The Associated Press and other news organizations.

Lhota, the ex-transit authority chairman and former deputy mayor to Rudolph Giuliani, defeated billionaire grocery magnate John Catsimatidis for the Republican nomination. Both Republican candidates largely pledged to follow Bloomberg's lead, focusing on maintaining the city's record low crime rates.

Another scandal-scarred politician, Eliot Spitzer, who resigned as New York's governor in 2008 after paying for sex with prostitutes, tried to run a self-financed campaign for the lesser office of city comptroller. But his distant, television-heavy campaign struggled to connect with voters and he lost to Manhattan Borough President Scott Stringer by a margin of 52 percent to 48 percent.

Bloomberg, the businessman Republican-turned-independent, is completing his third term. While the city's registered Democrats outnumber Republicans 6 to 1, the Republican Party's recent success in mayoral elections has been largely attributed to a crime epidemic, the aftermath of the Sept. 11 attacks or other extraordinary circumstances.

Nearly three-quarters of Democratic primary voters said the next mayor ought to move away from Bloomberg policies, according to the exit polls.

De Blasio, 52, has fashioned himself as the cleanest break from the Bloomberg years, proposing to raise taxes on the wealthy to fund universal pre-kindergarten and change city police practices he says discriminate against minorities.

De Blasio, who worked in Bill Clinton's White House and Hillary Rodham Clinton's Senate campaign before being elected to the city council and then public advocate, became the front-runner in the race's final weeks.

Quinn was the front-runner for much of the year, boasting the biggest campaign war chest and strong establishment backing. But she was dogged by her support to change term limits to let Bloomberg run again in 2009, a decision unpopular with liberals who make up the bulk of Democratic primary voters.