A three-man race became a two-way contest for the state senate seat representing Connecticut’s 10th district on Thursday, as Gary Holder-Winfield picked up the endorsement of an opponent, of the local arm of the Democratic Party and of Mayor Toni Harp.

A delegation of Democrats in the 10th District — which comprises the western half of New Haven and a sliver of West Haven — unanimously endorsed Holder-Winfield at Thursday’s nominating convention, winning him an automatic spot on the ballot. The endorsement came an hour and a half after Holder-Winfield picked up the support of his colleague, State Rep. Juan Candelaria, who ended his own bid for the senate seat just four days after announcing his candidacy.

Holder-Winfield now faces just one opponent, former Ward 30 Alderman Darnell Goldson, in a Feb. 25 special election for the 10th District state senate seat, which Harp vacated this month upon assuming the mayor’s office. Having promised to back the Democratic nominee, Harp will support Holder-Winfield as her successor. Holder-Winfield bowed out of the mayor’s race in favor of Harp last summer.

“I don’t worry about confident — I worry about work,” Holder-Winfield said after securing the unanimous endorsement of the 41 delegates present at the convention. “I’m going to go out and knock on people’s doors and talk to them. That’s my winning strategy.”

Currently a state representative for the 94th Assembly District, Holder-Winfield identified jobs, public safety and development projects as the central issues facing New Haven and West Haven residents. Students in four of Yale’s 12 residential colleges — Morse, Ezra Stiles, Pierson and Davenport — live in the 10th District, amounting to nearly 2,000 undergraduates, not including those living off-campus.

Holder-Winfield, 39, said his experience — five years in the General Assembly, spent moving major issues such as the elimination of the death penalty — best qualifies him to succeed Harp.

“Those are very big shoes to fill,” Martin Looney, who represents the other half of New Haven in the state senate, said Thursday. He, like Harp, will support Holder-Winfield as the Democratic candidate in the race.

Goldson, 52, blasted the endorsement process as “undemocratic” and said he still plans to petition his way onto the ballot. He said Wednesday he had already acquired the 272 signatures and planned to submit them Friday with the city’s registrar of voters.

He also said he should have been allowed to address the delegation, but that the Democratic “machine” had already made up its mind. He said he tried to call members of the convention to ask for their support but was unable even to make his case.

“Most of them didn’t call me back. I was shut out, but that’s OK. I expected that,” he said. “This is going to be fought on the streets. It’s going to be Darnell versus Goliath. It’s going to be biblical.”

Holder-Winfield responded to criticisms of the endorsement process by saying that each candidate had the same opportunity to talk to delegates. He said the procedure is the same one used for special elections across the state.

Both Holder-Winfield and Goldson pledged to participate in the state’s publicly financed Citizens’ Election Program, which awards candidates a matching grant of up to $63,750 if they successfully raise at least $11,250 in individual contributions between $5 and $100 from at least 225 people in the district. Holder-Winfield said he plans to begin fundraising Friday.

Throwing his weight behind Holder-Winfield, Candelaria called for Democratic Party unity, saying he was putting his own “aspiration for higher office on hold.”

Candelaria, who has represented the 95th Assembly District for 11 years, said his decision was informed by conversations with his campaign and with supporters. He met Thursday morning at City Hall with Harp and her chief of staff, Tomas Reyes, to discuss his decision, he said.

“2014 is going to be a tough election year for Democrats in Connecticut, and a fractured Democratic Party in New Haven is not what I want to see,” he said.

Should Holder-Winfield clinch the senate seat, his victory would leave open a spot in the House. Connecticut Gov. Dannel Malloy would then have 10 days to issue a writ of special election. Holder-Winfield said does not have a potential successor in mind.

Harp was first elected to the state senate in 1992.