Venezuela’s opposition won control of the National Assembly by a landslide on Sunday, delivering a major setback to the ruling United Socialist Party (PSUV) and altering the balance of power after 17 years of PSUV rule.

The opposition won at least 99 seats in the 167-seat legislature, National Electoral Council President Tibisay Lucena announced. The PSUV won 46 seats. The 19 remaining races remain up for grabs; if enough are won by the opposition, it could give the coalition a two-thirds supermajority needed to strongly challenge President Nicolás Maduro’s grip on power.

The streets of the Venezuelan capital, Caracas, broke out in shouts of joy and fireworks after the partial results were announced. In the plaza in wealthy eastern Caracas that was the center of last year’s bloody anti-government protests, a small group of opponents, some of them sipping Champagne, burned red shirts that are the obligatory revolutionary attire.

Within seconds of the results’ announcement, Maduro took to the airwaves to recognize the opposition’s win, saying that despite an adverse result for his party, Venezuela’s democracy and constitution triumphed. But he recalled the long history of coups in Latin America and blamed what he called a “circumstantial” loss on opponents who he said have been conspiring to destabilize his socialist revolution.

“I can say today that the economic war has triumphed,” he said in a televised address from the presidential palace.

Opposition leaders, meanwhile, spoke in strident terms, a prelude to what’s likely to be a period of intense political fighting in a country already deeply polarized.

Voter turnout was a stunning 74 percent, the highest for a parliamentary vote since compulsory voting ended in the 1990s, as Venezuelans punished Maduro’s government for widespread shortages, a plunging currency and triple-digit inflation that has brought the economy to its knees.

“Venezuelan families are tired of living the consequences of the failure,” Jesús Torrealba, the head of the Democratic Unity opposition coalition, told supporters at campaign headquarters. “The country wants change, and that change is beginning today.”

The opposition victory dealt a serious challenge to the socialist revolution started 17 years ago by Hugo Chávez, who until his death in 2013 had an almost magical hold on the political aspirations of Venezuela’s long-excluded masses.

It was also a major blow to Latin America’s left, which gained power in the wake of Chávez’s ascent but more recently has been struggling in the face of a regional economic slowdown and voter fatigue in some countries with rampant corruption. Last month, Argentines elected a conservative businessman over the chosen successor of left-leaning President Cristina Fernández, who was a close ally of Chávez’s. In Brazil, President Dilma Rousseff is battling low approval ratings and facing impeachment over a corruption scandal in her left-leaning Workers’ Party.

Before Sunday’s vote, mounting frustration with the Maduro government had thrust the opposition coalition Democratic Unity Roundtable (MUD) to a 30-point lead in polls.

Voting proceeded mostly peacefully through the day, though fears of unrest prompted some Venezuelans to line up before dawn so they could cast their ballots and get off the streets.

“There will be a new political landscape and balance of power,” said Luis Vicente Leon, the president of Venezuelan polling agency Datanalisis. “If the opposition wins and is smart, it will negotiate for change. But if opposition radicals take control who just want to get rid of the president, they will lose a golden opportunity” for reform.

That possibility of a new political landscape has generated excitement throughout Venezuela, an oil-rich nation of 30 million people, analysts say. But political leaders have expressed a sense of alarm. They worry that the government’s electoral defeat could spark violence similar to that of last year, when protests against Maudro — and counterprotests by his supporters — resulted in street clashes that left 43 people dead.

In the months leading up to Sunday’s vote, Maduro barred seven opposition politicians from running for office. The government has accused them of corruption or conspiring to overthrow the government. Dozens more are under arrest — held as “political prisoners,” according to MUD representatives.

The shooting death last week of regional opposition leader Luis Manuel Díaz, blamed on militias supporting the PSUV, heightened tensions. Maduro has denied any responsibility for violence.

The MUD opposition coalition has promised to force Maduro to loosen his grip on government institutions, including the Supreme Court and the National Electoral Council. Some among the loose-knit alliance of dozens of political parties have also promised a presidential recall campaign.

Al Jazeera and The Associated Press