Mayor Bill de Blasio’s job performance had so many voters seeing red that he inadvertently helped the GOP regain control of one of its last remaining Big Apple strongholds in southern Brooklyn, Democratic and Republican pols and pundits agree.

Republicans won the area’s congressional seat and, according to unofficial results, will pick up a state Senate and Assembly seat, and also retain a vacated Assembly seat.

President Trump’s popularity there wasn’t the only reason the Republican Party reversed a blue wave that swept through many of the area’s predominantly white, middle-class neighborhoods in 2018. Political experts and candidates said many constituents were motivated to come out and vote Republican because they’re fed up with rising crime rates under the Democratic mayor’s watch; his progressive policies that failed to address the city’s homeless crisis, and his handling of the COVID-19 crisis.

“I think people feel the city has swung too far to the left under de Blasio … and they’ve sent a clear message that they want law and order restored, they want to preserve our freedoms, and they want to put a stop to socialism,” said Republican Assemblywoman Nicole Malliotakis, who defeated Democratic incumbent Rep. Max Rose in the highly contested race for the 11th District congressional seat covering Staten Island and part of south Brooklyn.

Malliotakis, who lost to de Blasio in the 2017 mayoral race, prevailed despite Rose trying to distance himself from Hizzoner by calling him in one ad, “the worst mayor in the history of New York City.”

Although Democratic candidates fared well in some sections like Bay Ridge — including president-elect Joe Biden — most other parts swung Republican, especially in large Russian-speaking enclaves in Brighton Beach and Sheepshead Bay.

In the 22nd District state Senate race covering Bay Ridge east to Marine Park, Republican Vito Bruno, a nightlife legend, scored 54% of the ballots cast through Election Day while Democratic incumbent Andrew Gounardes collected 46%. Only two years ago, Gounardes pulled off a shocking upset over then-Sen. Marty Golden, a longtime Brooklyn Republican power broker.

Bruno credited the mayor for helping Republican campaigns.

“He’s probably the most unliked mayor ever,” said Bruno, who managed the former 2001 Odyssey club in Bay Ridge featured in “Saturday Night Fever.” “People out here have a lot of animosity toward him … and anyone tied to him got hurt.”

In the 46th District state Assembly race covering Bay Ridge east to Coney Island, relative unknown Republican Mark Szuszkiewicz declared victory over Democratic incumbent Mathylde Frontus, 54% to 46%.

Malliotakis’ Assembly seat — which includes a sliver of Bay Ridge besides part of Staten Island — will remain with the GOP as Republican Michael Tannousis handily defeated Democrat Brandon Patterson.

Both Gounardes and Frontus have yet to concede and are holding onto the slim hope they’ll retain their posts once thousands of absentee ballots are counted.

Heading into Election Day, Malliotakis was the only Republican elected official with a piece of Brooklyn.

Hank Sheinkopf, a Democratic political consultant, said his party is “going backward” in southern Brooklyn thanks to de Blasio turning off a constituent base that has historically favored police presence over protests.

“This is all about de Blasio and the growing anti-cop activity that has been allowed to fester under his watch,” he said. “More riots means more Republicans in office.”

Steve Saperstein, a former Republican-turned-Democrat who is a frontrunner in next year’s City Council race to represent Sheepshead Bay, agreed.

“The election results are a reflection of de Blasio’s catastrophically bad management of the COVID crisis,” he said.

Gov. Andrew Cuomo claimed Hizzoner’s job performance also provided the GOP with enough ammunition to prevail in key races upstate and on Long Island. However, critics have said Cuomo shares some blame, especially for his role in establishing the state’s controversial bail-reform laws.

Bill Neidhardt, a spokesman for the mayor, scoffed at the idea that de Blasio’s unpopularity helped Republicans at the polls.

“Oh please,” he said. “The mayor has been elected for decades off the support from a working-class coalition he built in Brooklyn. The Post, the GOP and corporate Democrats like to point fingers, but sticking a national trend on us is pathetic.”