BRASILIA — Brazilian President Luiz Inácio Lula da Silva ‘s comeback to win Brazil’s presidential runoff Sunday is already facing its first hurdle as his competitor, Sen. Flávio Bolsonaro challenges the results, setting the stage for a possible showdown between the country’s two polarizing political forces.

Lula, who convinced an extra 10 million voters to support him in the runoff, is expected to take office on Jan. 5, 2027 for his fourth non-consecutive term. He will serve as a counterweight in a region where leaders are shifting to the right and aligning with U.S. President Donald Trump. Bolsonaro, son of former President Jair Bolsonaro, promised to cozy up to the Trump administration.

In a press conference Sunday, Bolsonaro said he planned to request an annulment of the election following a chaotic extension of voting at the request of both candidates. However, it’s unclear what legal avenue he would seek to do that. His father also contested his loss to Lula four years ago and now serves a 27-year prison sentence for a coup attempt.

Early signs from Brazil’s institutions and from leaders across the region suggest the results will be respected nationally and internationally. Trump has yet to weigh in.

Even with the vote extension, Lula’s win was decisive. The soon-to-be 81-year-old incumbent won more than 64 million votes compared to just under 60 million for Bolsonaro, a margin of nearly 4%.

President of Brazil’s electoral authority, Kassio Nunes, who was appointed to the Supreme Court by ex-president Bolsonaro, was among those who recognized Lula’s victory Sunday.

“This is a really uphill battle for Flavio Bolsonaro. Important Brazilian power brokers are closing ranks behind Lula, sometimes begrudgingly,” said Brian Winter, Brazil analyst and editor-in-chief of Americas Quarterly.

“I sense that Brazilian power brokers that matter don’t really want to go down the path of a truly contested election,” he said.

Brazil holds general elections every four years, and its electronic voting machines have made the tallying process quick and secure.

Brazilian authorities adopted electronic voting machines in the 1990s to combat fraud and the system has been largely reliable since then. Results are usually reported mere hours after polls close.

In the lead-up to the 2022 vote, Jair Bolsonaro repeatedly cast unfounded doubts on Brazil’s electronic voting system. No significant fraud has ever been detected.

But the usually swift voting process was thrown into disarray Sunday after a last-minute decision to extend voting nationwide at both candidates’ requests.

Lula made the request because of issues with public transportation in metropolis Sao Paulo and northeastern city Salvador, two of his strongholds. Bolsonaro requested it after heavy rains in the south, which he won by a strong margin in the first round.

The decision was made by a Supreme Court justice mere minutes before polls were set to close at 5 p.m. and the speed of Brazil’s counting process meant many polling stations didn’t receive the news until they were already wrapping up.

Yet given the reliability of Brazil’s voting system and Lula’s win by a significant margin, a path to annul the results could be difficult for Bolsonaro.

Regardless, Lula still faces challenges moving forward, including political polarization in the country, a possible fiscal crisis and a right-wing Congress where Bolsonaro’s party will have more seats than any other.

“We shouldn’t underestimate the power of the Bolsonaro family,” Winter said. “They can make life difficult for Lula for weeks and months to come.”

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Savarese reported from Sao Paulo.