Argentina will face a run-off election next month after neither presidential candidate gained enough votes to win the poll outright, the BBC reports.
Centre-left candidate Daniel Scioli led exit polls, and just edged centre-right Buenos Aires mayor Mauricio Macri with most votes counted.
Many had expected Mr Scioli to lead by a greater margin.
The run-off on 22 November will be the first time an Argentine election will be decided by a second round.
With 86% of the votes counted, Mr Scioli was marginally ahead with 35.9% of the vote, while Mr Macri had 35.2%.
To win outright in the first round, a candidate needed 45% of the vote or a minimum of 40% as well as a 10-point lead over the nearest rival.
“What happened today will change politics in this country,” Mr Macri, the mayor of Buenos Aires, told supporters.
