Brazil’s left-wing President, Luiz Inácio Lula da Silva, and his right-wing rival, Senator Flávio Bolsonaro, have clashed in a debate held one week before the run-off presidential election.

Polls recommend the two candidates are neck and neck and the televised debate was hailed as a likelihood for both to sway undecided voters.

But the showdown was marked by private attacks and analysts have warned that its aggressive tone may improve the abstention price further.

In the first spherical of voting, held on 4 October, Bolsonaro defied opinion polls by securing a slender lead over Lula.

Sunday’s debate was the first of two before the vote. The second is deliberate for Friday, just two days before polls open.

Flávio Bolsonaro is standing for the Liberal Party after his father, Jair Bolsonaro – who ruled from 2018 to 2022 – was sentenced to more than 20 years in jail for plotting to overthrow Lula after the latter beat him in the 2022 election.

The youthful Bolsonaro won 47% of the vote in the first spherical, in contrast with Lula’s 45.2%, with both falling brief of the 50% of the legitimate votes wanted to stave off a decisive second spherical.

Since the return to democracy in 1988, there has been no occasion in which the candidate who lost in the first spherical went on to win in the second but Lula has instructed his supporters that he will “win in extra time”.

Analysts consulted by BBC News Brasil were struck by how much the debate was dominated not by points but private attacks.

Yuri Sanches from pollsters AtlasIntel said it was a debate in which no insurance policies were mentioned and there were no rational arguments.

“The independent voter, who is sometimes against Bolsonaro and sometimes against the Workers’ Party [of Lula], came out of it with a very negative impression.”

Lucas Aragão from political evaluation agency Arko Advice said Bolsonaro had appeared calmer during the debate and appeared to have managed to “get under Lula’s skin”.

Rafael Cortez from consulting agency da Tendências Consultoria, however, argued that Lula had managed to rating a aim when he said he would open up his monetary and cellphone information and these of his household to judicial scrutiny, and challenged his rival to do the same before Sunday’s run-off.

Many observers criticised the format of the debate, which was described as chaotic at instances, with each of the candidates pacing around the TV studio as the other was talking.

One heated trade saw Bolsonaro telling Lula he should come stand next to him so that the two could discuss.

Referring to alleged hyperlinks between the senator and paramilitary vigilante teams, Lula said “I don’t want to be close to you”, and that he needed to preserve “distance from the Bolsonaro family” and “the militia”.

Bolsonaro, who has dismissed the allegations as faux information, in flip tried to bait Lula by saying, “On second thoughts, maybe it’s better to keep my distance so that my wallet isn’t stolen.”

He also accused the Workers’ Party of being corrupt, holding up the palm of his hand on which he had scribbled “CORRUPTO” (Portuguese for “corrupt).