Fired-up Democratic Socialists of America progressives are bragging about their “special sauce” propelling Zohran Mamdani to the cusp of becoming New York City’s next mayor — as the contender increasingly refuses to say whether he’ll push their radical agenda.

The socialist group’s Big Apple chapter mobilized its already formidable field operations during the Democratic primary, recruiting 50,000 volunteers to help turn Mamdani from dark-horse candidate to the party’s landslide nominee, a recent The Nation report details.

The massive volunteer effort — which included more than 1.6 million door knocks and 2.3 million calls — relied on stirring up grassroots enthusiasm and organizing, which one local DSA official called the group’s “special sauce” in the report.

“We don’t gate-keep the skills you need to run a campaign,” NYC DSA co-chair Grace Mausser crowed to the magazine.

The army of unpaid true believers contrasted with former Gov. Andrew Cuomo’s top-down-style primary campaign, where even some of his paid canvassers reportedly openly supported Mamdani.

Mamdani ended up clobbering Cuomo in the June election, earning an historic number of votes in a win with political ramifications across New York City and the country.

While Mamdani’s viral social media videos often get credit for his meteoric rise, The Nation report indicates his victory was substantially helped by the NYC DSA’s ground game.

“Say what you want about DSA, but they can put an army on the street,” a city lawmaker, who spoke on condition of anonymity, told The Post. 

“They can knock on more doors in a weekend than most campaigns will knock in a month,” the pol said. “It’s no joke. Every campaign needs bodies and DSA has bodies.”

The DSA’s effort specifically targeted three groups — left-wing activists, tenants in the city’s 1 million rent-stabilized apartments, and Muslims — who’d be excited over Mamdani’s working-class-focused policies, the Nation report states.

The grassroots effort snowballed into a juggernaut of volunteer enthusiasm that money couldn’t buy – and could further spell doom for Cuomo’s and Mayor Eric Adams’ independent bids in November’s general election, insiders said.

“For Cuomo and Adams, it is truly difficult to go up against an army of volunteers who are fired up for a candidate against paid door knockers who are only motivated by their hourly wage,” a Democratic operative told The Post.

“However, the DSA volunteers will find out the hard way that their radical ideas have to face the realities of how the real world works in January,” when Mamdani would take office, if elected.

Chris Sosa, a Democratic consultant, said Mamdani ran the single-most impressive ground game he has seen, with the DSA at its core.

“The membership is deeply active, organized and strategic,” he said. “They punch above their weight and grow by the day. If you ignore the chatter and its most unpleasant online members, what you see are the hardest and most disciplined workers in politics.”

Mamdani’s primary win was fueled not only by voters in crunchy liberal Brooklyn neighborhoods, but also surprising gains among New Yorkers who don’t traditionally back democratic socialists.

But Mamdani, as he tries to maintain his front-runner status before November’s four-way general election, has increasingly been shy about sharing whether he rejects many radical NYC DSA policies.

The front-runner and his campaign have refused to respond on whether he supports the local DSA’s calls to end school safety officers in schools, release people jailed for drug crimes and sex work, and allow immigrants to vote and hold local office.

But Mamdani has also tried to distance himself from some of his past controversial views – such as defunding the police and refusal to denounce the “globalize the intifada” rallying cry – that could be unpalatable to general election voters.

Sosa predicted that Mamdani, if elected, will absolutely make some choices at odds with his DSA and other far-left backers.

“What interests me is how both sides of the equation, a Mayor Mamdani and empowered DSA, navigate this relationship,” he said. 

“It could be deeply productive and symbiotic. It could fracture. It could be tumultuous. But both sides want the best and are sober about the challenges ahead, so don’t be surprised if they find a way to navigate the growing pains.”

Not all insiders were convinced that Mamdani has the city’s DSA – which is distinct from the more extreme national Democratic Socialists of America organization – to thank for his position a stone’s throw from Gracie Mansion.

An Albany Democratic operative said the DSA’s ground game and organizing tactics aren’t new, but Mamdani’s ability to truly connect with voters is what made him a winningly effective contender.

“It’s Zohran himself,” the operative said.

“It’s smart campaigning, and again, it’s him. I don’t think that’s so much about secret, advanced DSA ground game tactics.”

Mamdani’s campaign didn’t return a request for comment Friday.

— Additional reporting by Vaugh Golden