NEW YORK — Democratic challenger Laura Gillen notched an upset Tuesday night over first-term GOP Rep. Anthony D’Esposito in New York City’s suburbs, flipping a highly coveted seat in a racially diverse district spanning the South Shore of western Long Island.

The win by Gillen, a former local government official, gives Democrats a much-needed boost in their quest to retake the House and returns some partisan balance in a region largely governed by Republicans at local and state levels.

Gillen, previously the town of Hempstead’s supervisor, had narrowly lost a bid against D’Esposito for the seat in 2022.

D’Esposito, a freshman member of Congress and former NYPD detective, faced scandal in the final months of his campaign after a September New York Times exposé revealed he had an affair and put his lover and his fiancee’s daughter on his payroll.

He has denied he violated House ethics rules.

Gillen’s path to victory was paved by Democrats’ outreach to Black and Latino voters in the district, her argument that she’s better positioned to work across the aisle and her message that her party cares about securing the border. Her prospects improved after Kamala Harris replaced Joe Biden at the top of the Democratic ticket.

Congressional races on Long Island, in the Hudson Valley and in central New York are expected to help determine whether Mike Johnson or Hakeem Jeffries serves as speaker next year.

In 2022, D’Esposito flipped the NY-04 red after former Democratic Rep. Kathleen Rice opted not to seek reelection.

It made the district one of a handful in the House where voters chose Biden in 2020 but elected a GOP House member two years later. The victory was part of a red wave that engulfed the state as Republicans flipped four New York House seats red.

D’Esposito, who was instrumental in getting then-colleague Rep. George Santos expelled, was a face of the storied Nassau County Republican Party and a leader that Donald Trump touted when he visited the district in September.

As one of the few women challengers Democrats floated in the battlegrounds of California and New York, Gillen proved to be a prolific fundraiser. She brought in $2.4 million in the third quarter of her campaign and $1.9 million in the second quarter.

Democratic attacks on D’Esposito often focused less on the accusations of patronage and nepotism and more on misconduct complaints against him that were lodged during his days as a police officer. He was accused of lying under oath, a matter New York City settled with $250,000 in taxpayer money, and he failed to secure his gun, which was stolen from him.

D’Esposito defended his police record in their sole debate. He accused Gillen of patronage and sought to use her record as town supervisor against her. He repeatedly attacked her as a liar, a gaslighter and someone he described as ineffective in the Hempstead government where they both served.

His ads targeted Gillen as an ally of unpopular Democratic leaders, Gov. Kathy Hochul and New York City Mayor Eric Adams, who he and other vulnerable New York Republicans painted as soft on migrants and crime.

“My opponent and Democrats throughout the country told us that the border was secure, and they said that the economy was booming,” D’Esposito said at the News 12 debate. “All of a sudden Kamala Harris becomes the nominee, and now they want to secure the border and they want to fix the economy. They’re lying to everyone.”

Gillen sought to paint D’Esposito as enabling a highly ineffective and dysfunctional Republican-controlled Congress, noting that House Republicans rejected the Senate’s bipartisan border deal.

“You send me to Congress,” she said in one ad. “I will work with anyone from any party to secure our southern border, lock up criminals pushing fentanyl and stop the migrant crisis.”

The Democrat also insisted that the GOP incumbent would green-light a nationwide abortion ban supported by Speaker Johnson.

D’Esposito, like other moderate Republicans fighting for their political lives in blue states, said he would not vote for a federal ban and accused Democrats of misrepresenting his views for political gain.

Democratic leaders stumped in the district for Gillen over the course of the race. They included House Minority Leader Jeffries, House Foreign Affairs Committee ranking member Gregory Meeks and House Minority Whip Katherine Clark.