By Brian Winter and Anthony Boadle SAO PAULO/BRASILIA (Reuters) – A tight runoff campaign for Brazil’s presidency kicked off on Monday with leftist incumbent Dilma Rousseff and pro-business rival Aecio Neves racing to win over supporters of the third-placed candidate after she was knocked out of the election. Neves, a centrist senator who had been widely written off until a few days before Sunday’s first-round vote, rode a late surge in support to grab second place with 33.6 percent of the vote. Rousseff led with 41.6 percent and they now face each other in an Oct. …