Castillo had a margin of 71,764 votes in his favor (8,735,448 against 8,663,684). The difference between Castillo and Fujimori reached more than 113,000 votes, however, it fell in this final stretch of counting.
The National Office of Electoral Processes (ONPE) said that it had so far counted 99.42% of the vote.
Of those, Castillo was the preferred candidate for 50.20% of voters, while right-wing candidate Keiko Fujimori was the preferred option for 49.79%.
The president of ONPE Pedro Corvetto said that turnout was 77% in the election.