A race that began with a surprise

When Brazil's presidential election runoff was set, Flávio Bolsonaro looked like the favourite. He had won the first round despite not leading most polls, and the gap between him and Lula was the narrowest ever recorded in a first round, at less than 2% of the vote.

The senator began the runoff campaign with a lead and the backing of most other defeated candidates, but instead of growing he stagnated. Lula, by contrast, has gained ground throughout the campaign, and the two now enter Sunday's contest virtually tied.

The two candidates

Lula, 81, has spent much of the runoff campaign focused on turnout, since abstention in the first round hit a record high and falls disproportionately on his own voters.

His opponent presents a very different profile:

• Flávio Bolsonaro is 45 and served as a congressman for more than 20 years, passing few bills
• He is the eldest son of former president Jair Bolsonaro, who is under house arrest serving a 27-year sentence for attempting a coup to overturn his 2022 defeat to Lula
• The senator has promised that if elected he will pardon his father
• He is under investigation in two federal police inquiries over alleged corruption and money laundering

What Bolsonaro promises and what voters say

Bolsonaro has vowed to "change the constitution and re-democratise this country", and his security agenda includes building five "mega-prisons" inspired by those of El Salvador's Nayib Bukele.

Voters on both sides see the choice in stark terms. Nuno Rau, a 63-year-old architect and writer, said: "We're facing two completely different projects for the country." He could not bring himself to vote for Bolsonaro.

Aparecida Moreira, a 62-year-old lawyer, will back Bolsonaro mainly because of the "iron fist" security policy he proposes. In her view, voting for Lula would amount to voting for justice Alexandre de Moraes, whom Bolsonaro supporters link to the president because he oversaw Jair Bolsonaro's conviction - even though the justice was not appointed by Lula.

How the race may be decided

With each side's supporters virtually "crystallised", the election will be decided by the small number of voters who identify with neither candidate.

Lula's late gains have come from a radically changed digital strategy and from student-led protests across the country, most of which did not involve the president. Political scientist Helcimara de Souza Telles argued that the turnaround has deeper roots: "In the first round, Lula's campaign failed to connect with the population, but now it has been civil society movements" driving his growth.

Both candidates drew large crowds to their final campaign rallies on Saturday in Rio de Janeiro, São Paulo and Belo Horizonte. The race is expected to be decided by a narrow margin among the 159 million voters of Latin America's largest country.

Many analysts believe that if Lula overturns his first-round defeat, Bolsonaro could follow his father's example from four years ago and refuse to concede.