Brazilians surprised many onlookers this month when they forced President Luiz Inácio Lula da Silva into a run-off election against Geraldo Alckmin.

Now, as the left-leaning incumbent prepares to face the candidate for the centrist PSDB in a decisive vote next Sunday, there are signs that the voters could deliver a second shock – one that could result in a significant shift in policy, with far-reaching implications for growth.