Santiago Peña of Paraguay's ruling conservative Colorado Party has won the presidential election, beating a centre-left challenger.
With almost all ballots counted, Mr Peña, an economist, got more than 42%, electoral officials say.
Efraín Alegre, candidate of the Concertación Nacional coalition, had nearly 28%. He later admitted defeat.
The Colorado Party has dominated the political scene in the landlocked South American nation for more than 70 years.
Sunday's presidential poll was decided in a single round of voting.
Addressing his supporters, Mr Peña, 44, said: "Thank you for this Colorado victory, thank you for this Paraguayan victory."
He also called for nationwide unity and consensus. Paraguay's economy is expected to grow by more than 4% this year, but the country has relatively high levels of poverty and corruption.
"We have a lot to do, after the last years of economic stagnation, of fiscal deficit, the task that awaits us is not for a single person or for a party," Mr Peña said.