Alejandro Giammattei will succeed corruption-tainted outgoing President Jimmy Morales, who leaves office in January.
With returns from 20 percent of polling stations counted, the preliminary results from the electoral tribunal gave centre-left candidate Sandra Torres 23.33 percent of the vote.
With 19 candidates in the race for president, and the winner needing an absolute majority, a runoff vote is likely in August.
In a country that produces enough food to feed 10 times its population, around eight percent of Argentinians can hardly afford one meal per day.
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