Nassau Republican Party chairman Joseph Mondello said Wednesday that Democrat Todd Kaminsky most likely has won a special election for state Senate against GOP candidate Christopher McGrath to fill the seat of former Senate Majority Leader Dean Skelos.

McGrath has not conceded, and Mondello urged elections officials to count nearly 3,000 absentee ballots before certifying the results.

Mondello said he was “not optimistic” that the absentee ballots, which favor Democrats, would change the outcome.

“I don’t see us being able to pull this out,” said Mondello, who pledged to avoid a long court battle. “In all honesty, we lost this race.”

Kaminsky (D-Long Beach) leads McGrath, an attorney from Hewlett, by 780 votes in unofficial returns in the race for the vacant 9th Senate District seat. Turnout was 28 percent.

Kaminsky, who declared victory Tuesday night, said the district, “has been without a senator for five months and the taxpayers deserve representation immediately. There is no reason the results of this election can’t be certified next week.”

advertisement | advertise on newsday

Whoever is declared the winner will only serve out the rest of Skelo’s term this year and faces another run for the seat in November.

Nassau County Board of Elections officials said 2,791 absentee ballots have been submitted but not yet counted. They include 1,318 from Democrats, 1,169 from Republicans and 206 from voters unaffiliated with any major party. Voters requested another 1,712 absentee ballots but have not yet returned them. The deadline is April 26.

“Barring any surprises that we don’t anticipate, there is no plausible result other than what happened last night,” said David Gugerty, Nassau’s Democratic elections commissioner.

John Ryan, counsel for Republican Elections Commissioner Louis Savinetti, said “all the votes must be counted.”

Mondello held out some hope for McGrath. He noted that the elections board must verify that voting machines operated correctly and did not produce any false results.

“I don’t think we can win, but what if we discover some serious problems with the machines?” said Mondello.

The county elections board will begin its count of absentee ballots on April 27, and expects to finish by the end of next week, Gugerty said.

In the interim, the board will collect the 266 electronic voting machines in the district and check for irregularities. Elections officials also will count any emergency ballots — cast when a machine breaks down — and affidavit ballots, which generally are cast when there are questions about a voter’s registration or address.

advertisement | advertise on newsday

“To ensure the integrity of this election, we think it’s important that all of the votes are counted,” said Senate GOP spokesman Scott Reif, responding for McGrath.

The outcome of the 9th District race could be crucial to control of the Senate. Republicans hold 31 of the 63 Senate seats but control the chamber thanks to a governing coalition with six breakaway Democrats, including Simcha Felder of Brooklyn, who sits with the Republican conference.

Gerald Benjamin, distinguished professor of political science at SUNY New Paltz, said a Kaminsky win would represent “a symbolic and substantive crevice in the solid Republican Long Island bloc.” Republicans have held all nine Long Island State Senate seats since 2010.

Sen. Michael Gianaris (D-Queens), chairman of the State Democratic Senate Campaign Committee, said a Kaminsky victory would give Democrats “big momentum,” heading into November.

Siena College pollster Steven Greenberg expressed doubt that the special election will have an impact on the fall races.

advertisement | advertise on newsday

“The elections in battleground Senate districts this fall will all be about local issues and local candidates in a high turnout presidential general election,” said Greenberg.