SAO PAULO, Sept 8 (Reuters) - A Nexus poll commissioned by BTG Pactual on Tuesday showed for the first time Brazilian right-wing Senator Flavio Bolsonaro slightly ahead of leftist President Luiz Inacio Lula da Silva in a simulated second-round runoff for next month's election, though they remain locked in a so-called technical tie.
If there was a runoff, the eldest son of former President Jair Bolsonaro would receive 46% of voter support compared with 45% for Lula, the poll said.
An August 31 poll had Lula leading Bolsonaro by 46% to 45%.
The result marked Bolsonaro's strongest showing since Nexus began tracking the race in late March, when the two were tied 46%-46%.
In a first-round scenario, Lula would lead with 39% of the votes, followed by Bolsonaro (35%), Augusto Cury (9%), Ronaldo Caiado (4%) and Renan Santos (4%), the poll said.
If no candidate wins more than 50% of valid votes in the first round, the two frontrunners advance to a runoff.
Nexus surveyed 2,002 people from September 4 to 7.
The poll has a margin of error of 2 percentage points -- greater than the expected difference between the candidates in the second round, a statistical tie.
First-round voting is scheduled for October 4, while a second-round runoff would be held on October 25.
