The leading candidate failed to collect 50% of the vote due to a strong showing from another group on the left, the Green Party. It's also interesting to note that two of the three leading candidates are women. BBC:
Brazil's presidential election will go to a second round after Dilma Rousseff failed to gain the 50% of votes needed for an outright victory.
With 98% of votes counted, President Lula's former cabinet chief has 47% with Jose Serra trailing on 33%.
The two will contest a run-off vote in four weeks' time.
A strong showing by the Green Party candidate, Marina Silva, who polled 19%, may have cost Ms Rousseff a first-round win.
