A survey published Tuesday shows that Brazilian voters could give government-backed candidate Dilma Rousseff an outright victory in the first-round presidential election on October 3. An opinion poll by the Sensus Institute put support for Rousseff, chief of staff and endorsed successor to outgoing Brazilian President Luiz Inacio Lula da Silva, at 50.5 per cent, enough to win office without a runoff, according to dpa. A distant second to the centre-left Rousseff was the 26.4 per cent of her closest rival, the centre-right candidate Jose Serra, a former Sao Paulo governor. The poll was based on 2,000 voter interviews in 136 municipalities across Brazil, with a margin of error of plus or minus 2.2 percentage points. The previous Sensus Institute survey late last month had Rousseff at 46 per cent and Serra at 28.1 per cent. Green Party candidate Marina Silva, a former environment minister under Lula, rose from 8.1 per cent to 8.9 per cent in the latest poll. If no candidate exceeds the 50-per-cent threshold, the presidency would be decided in a second-round election. Tuesday's survey found 55.5 per cent of voters would favour her in a runoff compared to 32.9 per cent for Serra. The opinion poll was sponsored by Brazil's National Confederation of Transport.