Horacio Cartes of the Colorado Party has been declared the winner of Paraguay's presidential elections by the South American country's electoral board.
Efrain Alegre, 50, a lawyer and career politician in the ruling Liberal Party, conceded defeat after several exit polls predicted a big win for his rival, 56-year-old Cartes, a millionaire businessman, in Sunday's election.
The country's electoral tribunal said citing results from 35 percent of polling stations that Cartes - with 46.1 percent of votes - was winning the election by more than nine percentage points over Alegre, with 36.9 percent.
Pollster Ati Snead's survey indicated that Cartes had won the election by capturing 44.4 percent of votes, with Alegre bagging 37.9 percent.
An exit poll by First Analisis y Estudios showed Cartes winning with 50.8 percent of votes versus 37 percent for Alegre.
A third exit poll showed Cartes with a nearly 21 percentage point lead over Alegre at 53.5 percent of votes, according to the Institute for Communication and Art.
Paraguay's 3.5 million voters also cast ballots on Sunday for the country's legislature and 17 governors.
Cartes is a political novice who never even voted before joining the Colorado Party four years ago.
He has pledged to reform his party, which was tainted by corruption during its 60-year reign through 2008.
Alegre's Liberal Party took over the presidency after withdrawing support for President Fernando Lugo and clearing the way for his impeachment in June.
The leftist coalition that swept him to power has since split, although Lugo was again on the ballot - this time as a Senate candidate.
Congress removed Lugo, a leftist and former Roman Catholic bishop, after finding him guilty of mishandling a botched land eviction in which 17 police officers and peasant farmers were killed.
Some of Paraguay's neighbours compared the two-day trial to a coup and imposed diplomatic sanctions on the South American nation.
Lugo's administration was also rocked by a sex scandal, after he was forced to admit to having fathered two children out of wedlock while he was still a priest, and he faces at least two other as-yet unresolved paternity suits.
Paraguay's current president, Federico Franco, is barred by the constitution from running for re-election even though he is just serving out what remained of Lugo's five-year term. He will hand over the presidency in August.
One of Paraguay's wealthiest men, Cartes primarily made his fortune in the financial and tobacco industries.
Rivals have tried to link him to drug running and money laundering, but he has never been charged with those crimes.
"The accusations made during this campaign have no truth to them, and personally I am very serene," Cartes said early on Sunday.
Al Jazeera's Mariana Sanchez, reporting from Asuncion on Sunday, said many voters told her they were disillusioned by Lugo and wanted the Colorado Party to return to power.
"I talked to many people here who wanted change and since they were disillusioned by Lugo, they said change meant going back to the very conservative Colorado Party," she said.
While Alegre has led corruption investigations in Congress, his reputation as an honest administrator was undermined by an investigation into whether he misappropriated state funds while serving as Lugo's public works minister.
"My leadership model is different from the traditional one. My project represents a 'decent Paraguay' versus the 'Paraguay of the mafias'," Alegre told Reuters news agency in a recent interview.
Polls were open from 7am to 4pm (1100 to 2000 GMT) and international observers said they had received no fraud complaints by midday.
There is no second round of balloting so the presidential candidate who captures the most votes wins. Voters also elected local authorities and members of Congress.
Once Cartes' victory is confirmed, Paraguay will have a right-leaning government, defying the trend in South America where leftists have made steady gains in recent years.
Only Colombia and Chile are ruled by conservatives.
Nearly 40 percent of Paraguay's 6.6 million people are poor. The landlocked country relies on soya-bean and beef exports, but it is also notorious for contraband trade and illicit financing.