SAO PAULO, Aug 11 (Reuters) - Brazil's President Luiz Inacio Lula da Silva's ‌advantage over Senator Flavio Bolsonaro in ‌a potential runoff ahead of October's general election narrowed, ​a CNT/MDA poll showed on Tuesday. Lula would receive 48.0% of the votes in a runoff, compared with 39.1% for Flavio ‌Bolsonaro, son of ⁠former President Jair Bolsonaro, according to the poll. In a June survey, ⁠Lula was seen with 49.3% of the votes, and Bolsonaro with 36.8%. If no candidate wins more than 50% ‌of valid votes in ​the first round, the ​two frontrunners ​advance to a runoff. (Reporting by Isabel Teles; Writing by ​Fernando Cardoso; Editing by Chizu ​Nomiyama and Keith Weir)