Mr Portillo, who was considered the front-runner in a field of 11 candidates in Sunday's election, stunned voters by confessing to a double murder in Mexico, but kept his loyal following.
With 65 per cent of votes counted, he won 48 per cent of the ballots, compared to 32 per cent for his rival, conservative businessman Oscar Berger, the former mayor of Guatemala City. However, it remained unclear last night whether he had captured enough votes to avoid a run off vote on Boxing Day.
Mr Portillo, 48, ran away with the lead after a day of suspense, during which results were delayed by an unprecedented high voter turn out.
Early returns showed that Mr Portillo's law and order opposition party, the Republican Front, was outpolled by less than 1 per cent by Mr Berger, candidate for the ruling National Advancement Party. Mr Portillo's camp blamed the results delay on the incumbent party.
The charismatic leader worries about human rights activists like 1992 Nobel laureate Rigoberta Menchu, who sees him as a stand-in for the the former military dictator, Efrain Rios Montt, and a catalyst for violence in the interior.
Yet Mr Portillo considers himself a populist in the mold of British Prime Minister Tony Blair, and apes the "Third Way" by offering a mix of welfare, state and free market policies to tackle Guatemalan class inequalities, inflation, and rising crime.
Known as "the Hoarse Chicken" for his speaking style, Mr Portillo turned his admission of shooting two Mexicans in self-defense in 1982 into a political advantage, proving candour and decisiveness. Detractors charged that Mr Portillo had not slain two attackers, as he claimed, but that he had gunned down unarmed students in a bar brawl. He was never prosecuted for the incident, and the case was declared inactive in 1995 by a Mexican judge.
Election day was free from the heavy military presence that overshadowed past polls, though hundreds of international monitors oversaw the voting in a "climate of fear", according to United Nations spokesman Bertrand de la Grange. UN officials also urged parties to abstain from violence "before, during and after the vote," though several disturbances in the rural interior marred peaceful elections.
The candidate of the former leftist guerrillas, Alvaro Colom, was expected to get less than 7 per cent of the vote, but the rebels' support in an alliance could secure a win for Mr Berger in December.
Mr Portillo, who has repeatedly described himself as a social democrat and an admirer of guerrilla icon Ernesto "Che" Guevara, has pledged his commitment to the UN-brokered peace accords.Reuse content