Former presidential candidate Marina Silva gave her endorsement to opposition presidential challenger Aécio Neves Sunday following Neves’ move to strengthen commitments to social policy within his platform. The endorsement came after Mr. Neves released a letter Saturday in which he agreed to carry out political reform as well as strengthen social and environmental policy proposals. In a statement published on her website, Ms. Silva said the commitments and her belief in the alternation of parties in power convinced her to giver her support to the candidate. “I will vote for Aécio and will support him, voting for these commitments, depositing faith in the sincerity of the proposals of the candidate and his party, and principally, delivering to Brazilian society the task to demand that they are complied with,” she said. She said her endorsement was not made in exchange for direct political appointments or favors. Mr. Neves came in second behind incumbent president Dilma Rousseff in a first-round election on Oct. 5, with 34% of the vote. Ms. Silva, the Socialist Party candidate, came in third place with 21% of the vote. Ms. Silva’s support for Mr. Neves was seen as critical helping convince undecided voters to back his candidacy. According to initial polls following the first round vote, Mr. Neves, of the Social Democratic Party, leads Ms. Rousseff, of the Workers’s Party, in support by a margin of 51% to 49%. The tow candidates are scheduled to face each other in a runoff election on Oct. 26.