The GOP appeared to have snagged a Bronx City Council seat in a major blow to the Dems in a local race where a controversial affordable housing development took center stage.

But when it came to one of the more contentious races, the Democrats cruised to victory in the newly minted 47th District in Brooklyn.

Republicans had their sights set on gaining ground in the heavily Democratic NYC Council. Political pundits believed the party had an advantage with redistricting, an expected low voter turnout and the shift by some in the city to the right.

The election, however, proved to be a wash for the GOP.

The unofficial results Tuesday evening showed Republicans are expected to maintain just 6 of the 51 council seats.

In the most stunning race, Republican Kristy Marmorato appears to have ousted incumbent Dem Marjorie Velazquez, according to unofficial results.

The win would make her the first GOP city councilmember lawmaker to represent the Bronx in more than 50 years.

Marmorato claimed victory with a 700-vote lead with almost all of the votes Tuesday night.

“I’m honored,” Marmorato told The Post on her way to her victory party.

Velazquez angered activists in her district last year when she abruptly reversed course and threw her support behind a 348-unit housing development on Bruckner Boulevard in Throggs Neck that required the City Council’s approval to upzone the site.

“Our people came out. Our voices were heard. It was about trust. The councilwoman could not be trusted anymore. They definitely trusted me,” said Marmorato, who vigorously opposes the Bruckner Boulevard rezoning project.

Lee Zeldin, who stumped with Mamarato over the weekend, called the results “amazing.”

“Kristy’s victory will send shock waves in and out of politics beyond the borders of The Bronx,” he said.

Velazquez, who held a significant edge in the money race throughout the campaign, had not conceded as of publication Tuesday evening.

In the marquee race heading into the day, Justin Brannan (D) easily beat out Dem-turned-GOPer Ari Kagan with more than 58% of the votes in the 47th District, according to unofficial tallies.

“My opponent was never burdened by the truth… just when I thought his team couldn’t go lower, he built a tunnel,” Brannan told supporters, including NYC Comptroller Brad Lander, at the Firefly bar in Bay Ridge.

Brannan also put Brooklyn Democratic Party Chairwoman Rodneyse Bichotte Hermelyn on notice after she took shots at him during the campaign giving fuel to his opponent.

“It was a disgrace… I think the county leader managed to unify the party in a way that she wasn’t expecting — we’re coming for her next!” he said.

Pols had thrown their hands up in recent weeks in predicting the race, saying there was no way to know how the new electorate would lean.

Meanwhile, in Brooklyn’s other newly drawn council area, the 43rd District, Democrat Susan Zhuang will win with Republican Ying Tan and Conservative Party nominee Vito LaBella splitting the GOP vote, unofficial results show.

In the District 19 rematch, firebrand Republican Councilwoman Vickie Paladino knocked off Tony Avella (D).

In the heavily Asian 20th district that includes Flushing and Fresh Meadows in Queens, incumbent Sandra Ung beat Republican Yu-Ching James Pai in another rematch.

The council, which passes legislation and has some oversight powers over city agencies, has long been dominated by Democrats and the party is certain to retain firm control when the final votes are tallied.

But several Republicans were still vying to unseat their Democratic incumbent rivals after making inroads in more moderate districts.

The GOP’s representation on the City Council has doubled from 3 to 6 out of 51 in recent elections due, in part, to redistricting and many Asian voters shifting to the right.

Hank Sheinkopf, a veteran New York-based political strategist, told The Post turnout for the election was “lousy.”

“This is not a day to take pride in the NYC election process because no one is out,” he said. “It’s patently a waste of money and time.

“But it does make politicians feel good.”

Additional reporting by Emily Crane, Jared Dowling, Steven Vago and Kevin Sheehan