(CNN) In an unexpected turn that rankled the party's left flank, Democratic National Committee chairman Tom Perez on Thursday endorsed New York Gov. Andrew Cuomo's re-election bid.

His announcement, at the party's state convention on Long Island, comes in the midst of a feisty primary campaign between Cuomo and actress Cynthia Nixon.

"You've been delivering results that have made people's lives better," Perez said in his speech. "That's why Andrew Cuomo and (New York Lt. Gov.) Kathy Hochul are charter members of the accomplishments wing of the Democratic Party, and that's why I'm proud to endorse them."

Perez's nod came alongside endorsements for Cuomo from 2016 Democratic nominee Hillary Clinton and former Vice President Joe Biden. The one-two-three punch of prominent establishment leaders arriving at the convention to publicly back Cuomo angered Nixon supporters and dredged up grievances tied to the 2016 presidential primary, when the DNC's national apparatus favored, though never openly endorsed, Clinton over Vermont Sen. Bernie Sanders.

"Perez coming in at this time only further drives a wedge in the Democratic Party," said Jonathan Westin, the executive director of New York Communities for Change, a progressive activist group supporting Nixon. "What we're seeing play out, in a microcosm here in New York, is that the party elites are out of touch with where the base of the party is at."

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