INCUMBENT Ricardo Nunes will face left-wing lawmaker Guilherme Boulos in a run-off to decide the next mayor of Sao Paulo, Brazil.

It follows Sunday’s first round of voting in Brazil’s local elections.

Rightwinger Mayor Nunes won 29.5 per cent of the vote.

He just edged out housing rights campaigner Mr Boulos, who gained the support of 29 per cent of the voters.

Far-right candidate Pablo Marcal just missed out on making the October 29 run-off, winning 28.1 per cent of votes.

He headlined the news for weeks after another candidate, Jose Luiz Datena, slammed him with a metal chair during a televised debate following references to sexual misconduct. 

"Watching the debates, there were often things that I didn't expect to happen, like the chair-throwing or the name-calling.

“I found it a little disrespectful to the public,” voter Joao Victor Caputo said after casting his vote in Sao Paulo.

Mr Nunes had the support of former hard-right president Jair Bolsonaro, while Mr Boulos was backed by President Luiz Inacio “Lula” da Silva. 

In Rio de Janeiro, incumbent Mayor Eduardo Paes, supported by Lula, was re-elected for a fourth, non-consecutive term, after winning an absolute majority of votes in the first round.