Argentina's presidential election is headed for a November 22 runoff between incumbent Cristina Kirchner's chosen successor Daniel Scioli and conservative rival Mauricio Macri.
Partial results indicate business favourite Macri leads the count with 36 percent of the vote to 35 percent for Scioli, with just more than two-thirds of polling stations reporting.
However, most results from Scioli's stronghold, Buenos Aires province, had yet to arrive.
Under Argentine electoral law, in order to win outright, a candidate must claim more than 45 percent of the vote, or at least 40 percent with a margin of 10 points over the runner-up.
The runoff will be the first in the country's history.
The South American country adopted a two-round presidential election system in 1973, but has never had a race go all the way to the second round.
The third-place candidate was Sergio Massa, a former Kirchner ally who fell out with the president and launched rival party the Renewal Front.
He had 21 percent of the vote.
The elections turn a page on 12 years under Kirchner and her late husband Nestor, who came to power in 2003 in the wake of a devastating economic crisis.
The Kirchners presided over a remarkable economic turnaround that saw average annual growth of more than eight percent during Nestor's presidency.
But the country is facing recession next year, according to IMF forecasts.
Macri has vowed to dismantle the Kirchners' legacy of protectionism, hands-on management of the economy and combative rhetoric.
Even Scioli has promised a change in style to attract more investment and increase productivity.