RIO DE JANEIRO — Brazil's deeply polarizing presidential election, which has pitted populists from opposite ends of the political spectrum — right-wing President Jair Bolsonaro and left-wing former president Luiz Inácio Lula da Silva — will go to a second round after no candidate secured enough votes Sunday to claim outright victory.

In a race that voters, analysts and the candidates themselves framed as an existential moment in Latin America's largest country, Lula, a former union leader who served two terms as president from 2003 to 2010, won a narrow plurality. But it was not enough to defeat Bolsonaro, who ended the night with a far more significant share of the vote than many polls predicted.

Brazil now enters a potentially destabilizing four-week period as the field of 11 candidates collapses to just Lula and Bolsonaro, political giants here who share a deep personal enmity and have warned of apocalypse if the other wins.

Lula, 76, running on a campaign of nostalgia with appeals to the working class, has framed the contest as a test of the strength of Brazil's young democracy. He calls Bolsonaro a threat to the system instituted after the military dictatorship fell in 1985.

Bolsonaro, 67, a former army captain who has lamented the collapse of the dictatorship, staffed his administration with present and former military commanders and attacked the country's civic institutions, has in recent weeks run a scorched-earth campaign. He has warned that Lula would lead Brazil down a path to socialism and ruin — turning the country into another Venezuela, racked by corruption and violence.

The election has drawn global attention as the newest venue for the worldwide struggle between democracy and authoritarianism. It has been watched particularly closely in the United States, where the politics are similarly polarized.

Now the contest won't be settled until Oct. 30, when Brazil will vote a second time.

With more than 99 percent of the vote counted Sunday evening, Lula had more than 48 percent of the vote, according to Brazil's Superior Electoral Court, nearly five percentage points more than Bolsonaro. But Lula wasn't cheering the result.

"Yesterday, I said that in every election, I want to win in the first round, but it's not always possible," he tweeted Sunday evening. "All of the polls put us in 1st place, and I always thought we would win. And we will. This is just a delay."

Bolsonaro had not spoken Sunday evening.

Lula's first-round plurality Sunday doesn't ensure him a second-round victory. Front-runners often reach their ceiling in the first round. And four more weeks of campaigning will probably boost Bolsonaro, who could benefit from an improving economy and falling unemployment and inflation.

"The entire world is saying that Bolsonaro has little chance of winning," said Renato Sérgio de Lima, director of the Brazilian Forum on Public Safety, a public safety think tank. "But I would say it's not that way: He will do whatever he can to destroy Lula. Any unthinkable thing could happen."

For many Brazilians, the unthinkable already has happened. For months, polls have consistently shown that Bolsonaro would lose — and lose badly. "Lula has a 14 point advantage," read the front-page headline of O Globo on Sunday.

His supporters seized on his performance as vindication. For weeks, Bolsonaristas have said the large crowds that assemble to see the president are far more impressive than any survey.

"I don't believe in polls," said Daniel Silveira, a federal congressman who has been accused by law enforcement officials of attacks against democracy. "The streets say it all. Polls say nothing."

Lula supporters reacted with dismay as a vote that many expected to be a clear victory become a muddied affair. Their candidate won the most votes. But after a first-round victory had seemed for weeks within reach, the outcome felt like a loss.

"Sad," said Leticia Bernardi, a Lula supporter who was waiting outside the São Paulo hotel where the candidate was to speak. "It's a defeat for democracy and a victory for fascism."

In Brasília, a Bolsonaro stronghold, the president's supporters, clad in the yellow and green of Brazil's flag, thronged the main promenade.

The prospect of four more weeks of campaigning and division disappointed many voters.

"I had really hoped this had all ended tonight," said Rafaela Machado, a 41-year-old nutritionist at the Esplanade of Ministries on Sunday. "But it's clear that the people in this country like to suffer."

The election in recent weeks has shaped up into a may-the-least-disdained-win contest. Both candidates have messianic followings, but each carries extraordinary political baggage.

Lula is a former shoeshine boy who rose from extreme poverty in Brazil's drought-punished northeast to become a metalworker and union leader who ultimately led his Workers Party to four consecutive presidential victories. But the charismatic politician came to typify the corruption that tarred his party and eventually led to his own imprisonment. The Brazilian supreme court annulled his convictions last year on grounds that the trial judge had been biased against him, but many Brazilians remain convinced that he's a thief.

But Lula's apparent advantage was that he was running against Bolsonaro, whose coalition began to fracture almost as soon as it coalesced, broken apart by a devastating pandemic that he mocked and dismissed, the ensuing economic crisis he struggled to contain and some damaging political blows he inflicted upon himself.

The country will now plunge into what might be its most politically uncertain moment since it left the yoke of dictatorship. The fear that many people already felt going into this election — a fear of violence, a fear for the country's future — will only heighten in the weeks to come. There have already been violence and killings between Bolsonaro and Lula supporters.

"People aren't talking about politics for fear of being shot," Lima said. "They aren't walking around with their candidate's shirt for fear that they will be beaten."

Heightening the tension has been Bolsonaro's campaign to undermine confidence in the vote. For months, he has campaigned as much against Brazil's electoral institutions as he has Lula. He has assailed the voting process as unverifiable without offering evidence. He has claimed the same people who released Lula from prison will be counting the country's votes. And he has vowed not to accept any result from elections he didn't deem "clean."

Many of his supporters have been primed to distrust any vote that doesn't go his way.

"There was fraud," declared Alvaro Corbellion, 59, a retired farmer on the Esplanade in Brasília. "Where are these alleged Lula voters? They are nonexistent. They are nowhere to be seen."

If Bolsonaro is defeated, he said, he was ready to "take up arms" and fight in a civil war.

"Brazilian people are peaceful," he said. "But our patience has limits."