Bolsonaro, son of former president Jair Bolsonaro, led Lula in the first round of the election earlier in October, but opinion polls have shown the two candidates about even after the gap between them narrowed.
Bolsonaro and Lula repeated their campaign proposals during the over two-hour debate hosted by Globo, Brazil's most-watched TV channel, focusing on themes such as the cost of living, welfare and security, while exchanging allegations of corruption.
Lula, who is seeking his fourth term after winning back the presidency in 2022, has defended his government's above-inflation minimum wage increases and stressed that his administration helped millions of Brazilians to escape hunger.
The president said the younger Bolsonaro "is like students studying for college entrance exams. They can memorise things, but they can't learn."
He also said that "in the gated community where Bolsonaro lives, people don't go hungry".
Bolsonaro responded by saying food prices for Brazilians rose during Lula's administration, and he criticised a tax reform approved by the current government, projecting the new rules would raise the tax burden on consumers.
"Lula doesn't even remember the last time he went grocery shopping because he lives in a luxury palace now."
The two candidates mostly limited the discussion to pre-established themes in the first few segments of the debate, toning down the personal attacks that marked the only previous debate in the campaign between the two.
At one point, Bolsonaro apologised to Lula after saying the president gives to Brazilians with one hand but "takes away with nine fingers".
Lula lost his left little finger in an accident while working as a lathe operator in a factory.
"I will not accept some rich guy, with a highly questionable political practice, calling me 'nine fingers,'" the incumbent said, demanding a retraction.
"Lula, if I offended you by calling you 'nine fingers,' then I sincerely apologise, I sincerely apologise," Bolsonaro said.
But he added: "Will you apologise to Brazilians suffering from insecurity ... in debt?"
The discussion heated up in the last minutes of the debate, when both candidates were allowed to interact without moderation, as Lula and Bolsonaro sought to link each other to the fraud involving lender Banco Master.
Lula pressed Bolsonaro on alleged links to the bank's jailed banker Daniel Vorcaro, and Bolsonaro questioned Lula about accusations involving his son and a pension fraud.
The debate was one of the campaign's final events, as Brazilian electoral law bars the candidates from broadcasting radio and TV campaign advertising starting on Saturday.
They can still hold rallies until the final hours of the day.
