Brazil's PSB party to back Neves in October 26 runoff - spokeswoman
The decision by the Brazilian Socialist Party increases the likelihood that the bulk of Silva's 22 million votes would go to Neves and increase his chances of defeating Rousseff.
The party's executive board voted overwhelmingly to support Neves, with 21 in favour. Only one board member voted to support Rousseff and seven voted to remain neutral.
Silva, who came third in Sunday's first-round vote, is expected to endorse Neves on Thursday after meeting with the parties that backed her bid.
(Reporting by Anthony Boadle)