"While the Nixon campaign has talked about increased turnout among new, young and more progressive voters, it doesn't appear that that will help her," said Greenberg.
Nixon's campaign hit back, saying that US polls had time and again missed a "new electorate" who have traditionally sat out the primaries but who are now energised by opposition to Donald Trump's presidency.
"Andrew Cuomo knows this race is tighter than this poll suggests, or he wouldn't be spending half a million dollars a day against us," said campaign spokeswoman Lauren Hitt. "Given how much money he's spent, it's hardly shocking that Cuomo would have expanded his lead with the establishment voters these polls capture."
A New York State Democratic Party mailer over the weekend that implied Nixon was anti-Semitic, without basis, sparked a furious backlash and forced an apology, with Cuomo denying that he had any knowledge of it.
Nixon, who has Jewish children and went to synagogue to celebrate the Jewish New Year on Sunday, has accused Cuomo of orchestrating a smear campaign.