Right-wing Senator Flávio Bolsonaro led President Luiz Inácio Lula da Silva in the first round of Brazil's presidential election on October 4, partial results showed, setting up a widely expected runoff between the two on October 25.

With more than 99% of polling stations processed, Bolsonaro had 47.2% of valid votes against 45% for Lula, according to Superior Electoral Court (TSE) figures. Neither candidate is on track to reach the 50%-plus-one threshold needed to win outright.

Bolsonaro's lead has narrowed through the night as votes from Lula's stronghold in the poorer northeast were counted. In 2022, Lula overtook Jair Bolsonaro only after 70% of the vote had been counted, finishing the first round with 48.4% against 43.2%.

The result marks a stronger showing for the former president's eldest son than polls had suggested. On the eve of the vote, a Datafolha survey put Lula ahead with 45% of valid votes against 42% for Bolsonaro, a statistical tie, Folha de S. Paulo reported.

Bolsonaro appears to have benefited from strategic voting by right-wing voters, after spending weeks urging supporters to back the only candidate who could beat Lula. Psychiatrist and author Augusto Cury, Renan Santos and Ronaldo Caiado each had less than 3% of the vote.

Those eliminated candidates, mostly on the right, together hold more than 7% of the vote, narrowing Lula's path to victory in the runoff.

Lula followed the count at a hotel in Sao Paulo alongside Vice President Geraldo Alckmin, former President Dilma Rousseff and Workers' Party (PT) president Edinho Silva. The mood in his camp was one of apprehension, Valor reported, as allies had been counting on a wider first-round lead.

Bolsonaro reacted to the result by saying he was "very happy with the real possibility that, three weeks from now, Brazil will give a definitive answer by choosing a modern government."

Lula, meanwhile, described the outcome as "unexpected," saying he had been confident he would "win in the first round."

The seasoned leftist leader added, "Tomorrow we start a new campaign," and remarked, "I am very good in the knockout stage."

No Brazilian president has been elected in the first round since 1994.

In the state of Sao Paulo, the country’s richest and most populated, right-wing Governor Tarcísio de Freitas was re-elected in the first round, defeating PT candidate and former Finance Minister Fernando Haddad.

With 90.04% of the vote counted, Tarcísio had 62.85% of valid votes against 36.22% for Haddad, Estadão reported. It was the first time since 2014 that the Sao Paulo race had been decided in the first round.

The comfortable win positions Tarcísio, once seen as a potential successor to Jair Bolsonaro in this year's presidential race, as a likely contender in 2030. Bolsonaro's campaign expects the governor to throw himself into the national runoff.

For Haddad, seen as a possible successor to Lula within the PT, it was a fourth consecutive electoral defeat.

Bolsonaro's Liberal Party also performed strongly in Senate races, securing 16 of the first 25 seats decided.

Former first lady Michelle Bolsonaro was elected senator for the Federal District.