Uruguay will have to wait a few more days to find out who will emerge as the winner of Sunday's presidential election.
"There was never such a tight ballot," Jose Arocena, head of the country's Electoral Court said.
With almost all of the ballots counted, the conservative National Party's Luis Lacalle Pou, who is 46, has about 30,000 more votes than ruling leftist Broad Front's Daniel Martinez, who is 62.
Opinion polls since October's first round had indicated that Pou would comfortably win the run off.
Uruguayan presidents are not allowed to serve consecutive terms, but Broad Front has been at the helm of the country since 2005.
Outgoing president Tabare Vazquez said Uruguay will not fall victim to the turmoil some South American countries are experiencing. He predicted a smooth transfer of power.
"The people of Uruguay can rest assured that we are going to achieve this," Vazquez said.
Despite the polls predicting that the center-right Pou would win, Jenny Pribble, an associate professor of political science at the University of Richmond in the United States, said Broad Front remains popular. "Their signature policy initiatives - public health expansion, the creation of a national care system, marriage equality and the legalization of abortion and cannabis - advanced citizen rights and have earned the party a strong following."
A slowing economy, rising unemployment and crime were the major issues of concern to voters.
Results are not expected until the end of the week.