SAO PAULO, Aug 3 (Reuters) - Brazilian President Luiz Inacio Lula da Silva and Senator Flavio Bolsonaro are running neck and neck ahead of October's presidential election, a Nexus/BTG Pactual poll showed on Monday, as the right-wing lawmaker narrowed the gap with the leftist incumbent.
In a simulated second-round runoff, Lula would receive 46% of voter support compared with 45% for Bolsonaro.
A July 27 Nexus poll had Lula leading Bolsonaro 47%-43%.
In a first-round scenario, Lula would lead with 41% of the votes, followed by Bolsonaro (37%), Ronaldo Caiado (5%), Renan Santos (4%), and Romeu Zema (3%).
The previous poll showed Lula at 42% and Bolsonaro at 33% in the first round.
If no candidate wins more than 50% of valid votes in the first round, the two frontrunners advance to a runoff.
Lula, 80, was officially named the Workers' Party candidate for a fourth non-consecutive term on Sunday, pledging to boost defense investment and safeguard Brazil's rare earths.
Nexus surveyed 2,002 people between July 31 and August 2; margin of error 2 percentage points.
(Reporting by Gabriel Araujo; Editing by Kirsten Donovan )