Polls close in key Mexican vote, both main contenders declare victory

Governor candidate Alfredo del Mazo (C), of the Institutional Revolutionary Party (PRI) delivers a message to the media next to his wife Fernanda Castillo (R) and Campaign coordinator, Ernesto Nemer, during the election day for governor for the state of Mexico in Toluca, Mexico June 4, 2017. REUTERS/Carlos Jasso

TOLUCA, Mexico (Reuters) - Mexico's ruling Institutional Revolutionary Party (PRI) likely won a key state election on Sunday by a slim margin, according to an official preliminary projection of results that was quickly challenged by the leftist party seen in second place.

An early count from the State of Mexico's electoral institute projected PRI candidate Alfredo del Mazo as winning between 32.75 percent and 33.59 percent of the vote.