Former Mayor Ed Koch stumped for Bloomberg at a subway stop early Wednesday and the Uniformed Firefighters Association union announced it was endorsing the Democrat, City Comptroller William Thompson Jr.
Meanwhile, the four candidates competing in two runoffs -- for city comptroller and public advocate -- readied for another two weeks of campaigning.
With fewer than 50 days to go until the general election, Thompson -- who faces a popular billionaire mayor -- has no time to waste.
Before polls had even closed in Tuesday's primary, Thompson had already forgotten about his Democratic opponent and was campaigning hard against Bloomberg, telling voters now is the time to unseat "the richest person in New York City."
"Mike Bloomberg's been there for wealthy New Yorkers," Thompson told voters in Queens. "He's been there for Wall Street, he's been there for big corporations. We need somebody who's going to stand up and fight for us."
Thompson became the Democratic mayoral nominee after clobbering Tony Avella, a city councilman from Queens. With 100 percent of precincts reporting, Thompson had 70 percent to Avella's 21 percent.
Bloomberg, who is not registered with any party, did not compete in a primary.
The former Republican held his own campaign rally Tuesday night anyway. He did not mention Thompson by name, but he said voters have a choice of progress or "politics as usual."
Democratic mayoral primaries are typically crowded in left-leaning New York City, but this year it was a lonely affair.
A few would-be candidates changed their plans after Bloomberg reversed his long-held support for term limits last year and convinced the City Council to extend the law so he could run again.
Thompson struggles with a major money disadvantage -- he raises it, while Bloomberg spends his own, blowing through more than $40 million so far. Thompson has about $6 million.
Voters also consistently give Bloomberg high approval ratings in opinion polls. But Thompson may be able to exploit one weakness.
Some Democratic voters said Tuesday that they had once supported Bloomberg, but would not vote for him in November because of the way he changed the term-limits law. Voters twice supported term limits through referendums in the 1990s.
Sharda Laier, a jewelry designer who voted for Thompson on Tuesday, said she has supported Bloomberg in the past but won't anymore.
"I don't like this idea of changing the term limits, I really don't like it," Laier said. "I think it's wrong to have someone there in that position for as long as he thinks he should be there."
Two other citywide races were headed for runoff elections Sept. 29.
In the tight New York City comptroller race, no candidate appeared likely to get the 40 percent needed to avoid a runoff. The city Board of Elections could take several days to finish counting votes, including about 9,500 absentee ballots.
The top two vote-getters in the four-way race, with 100 percent of precincts reporting, were City Councilman John Liu with 38 percent of the vote and Councilman David Yassky with 30.5 percent.
The comptroller is the city's chief financial officer, analyzing the budget and auditing city agencies. The comptroller also oversees the $80 billion municipal pension system.
The race for New York City public advocate was also headed for a similar fate. None of the four Democrats competing reached 40 percent.
Councilman Bill de Blasio had about 33 percent of the vote compared to 31 percent for Mark Green, who was elected the city's first public advocate in 1993.
The public advocate is the ombudsman for City Hall, and is next in line if something happens to the mayor.
Turnout was light Tuesday in local primaries throughout the state.
Statewide, 13 counties had local elections, including primaries for mayor in Albany, Buffalo and Syracuse. Buffalo Mayor Byron Brown survived a primary challenge from City Councilman Michael Kearns, essentially winning another term because there are no Republican or independent challengers.
Voters in Queens chose Democrat Mike Miller to fill an Assembly seat vacated by Anthony Seminerio, who pleaded guilty to a federal corruption charge. Republican Donna Marie Caltabiano lost that special election.
In Manhattan, three candidates competed in the primary for what is known as the most high-profile prosecutor job in the country.
Defense lawyer and political scion Cy Vance won the primary. With no Republican challenger, he is effectively Manhattan's next district attorney.