One of the most unpredictable and contentious primary campaigns the city has seen in decades is drawing to a close. And on Tuesday, for the first time since 1997, voters will not see Michael Bloomberg’s name on their mayoral ballot.

Bloomberg has defined New York City for 12 years, largely setting party politics aside as he led with his data-driven convictions and his immense fortune. Both parties are now grappling with his legacy – the Republican mayoral hopefuls are largely promising to maintain his policies, while the Democrats have offered a sharply different approach.

Their front-runner is pitching himself as the cleanest break with the current administration.

Bill de Blasio, the public advocate, enters primary day with a commanding lead in the polls, a staggering reversal of fortune from six weeks ago, when his campaign was mostly an afterthought. But several events coincided to give him momentum in the race’s final days:

_ He fought a proposed closure of a Brooklyn hospital, even getting arrested for his efforts, which gave a much-needed shot of publicity.

_ His interracial family, especially his Afro-sporting 15-year-old son, became the center of his advertising campaign. That prompted Bloomberg to call de Blasio’s campaign “racist” in an interview released over the weekend, putting de Blasio’s rivals in the unwelcome position of having to defend the public advocate.

_ And former front-runner Anthony Weiner succumbed to another sexting scandal, prompting many of his supporters to defect to de Blasio, another scrappy, progressive candidate hailing from outside of Manhattan.

In a Quinnipiac University poll released Monday, de Blasio was the choice of 39 percent of likely Democratic voters, just shy of the 40 percent mark needed to avoid triggering an automatic Oct. 1 runoff between Tuesday’s top two finishers. One poll last week had him over 40 percent, but the campaigns believe that a runoff is likely.

De Blasio has adopted the mantle of the clear favorite. But that Quinnipiac poll, which surveyed 782 Democrats and has a margin of error of 3.5 percentage points, also suggested that 18 percent could change their minds before entering the voting booth.

Quinn, who is bidding to become the city’s first female and first openly gay mayor, led the polls for most of the year but has seen support disappear as her rivals have repeatedly linked her to the bitter debate to let Bloomberg run for a third term in 2009.

The mayor’s opponent that year was Thompson, who stunned the political world by nearly upsetting the billionaire incumbent. The race’s lone African-American, Thompson has said he is counting on winning the bulk of black and Latino voters to propel him to the runoff.

Election experts estimate that minority voters will make up more than half the Democratic primary electorate. Most polls have Quinn and Thompson within a few points of each other.

Weiner jolted the race in May when he ended his self-imposed political exile that began when he resigned from Congress in 2011 after sending lewd online messages to women who were not his wife. He led the polls for nearly a month only to tumble when it was revealed that he had continued to send the explicit messages in the months after leaving office.

The comptroller, John Liu, is bidding to become the city’s first Asian-American mayor but has been dogged by a fundraising scandal. He has been polling in the single digits.

Republicans will look to continue an improbable winning streak. Though outnumbered by Democrats in the city 6-to-1, the GOP has won the last five mayoral elections. (Bloomberg was an independent running on the Republican line four years ago.)

Joe Lhota, the former MTA chairman who received acclaim for steering the transit agency through Superstorm Sandy last fall, has led the polls all campaign. A former deputy mayor to Rudolph Giuliani, Lhota has pledged to maintain the city’s record low crime rates.

His primary challenger is John Catsimatidis, a billionaire grocery store magnate who has unleashed a series of blistering attack ads on Lhota, including one that mocks the front runner for dismissing Port Authority police officers as “mall cops.” Catsimatidis has spent more than $4 million of his own money on the race, but that’s a far cry from the $102 million Bloomberg spent four years ago.

Also Tuesday, ex-Gov. Eliot Spitzer will be trying to make a political comeback in the Democratic primary for city comptroller. Seeking to rebuild a political career devastated by a prostitution scandal, Spitzer is taking on Scott Stringer, Manhattan’s borough president.

Polls open at 6 a.m. and close at 9 p.m. Experts do not believe turnout will be high.

(AP)