Mr Pena Nieto, secured between 37.9 and 38.55 per cent of the vote, ahead of second-placed leftist challenger Andres Manuel Lopez Obrador, who had between 30.9 and 31.86 per cent of the vote, the official quick count showed.
The 45-year-old former governor, who is married to one of the country’s most popular soap opera actresses, is a young face on an old party.
The PRI, once described as “the perfect dictatorship”, ruled Mexico for 71 years until finally being cast out in 2000 by an electorate exhausted after decades of corruption, backroom deals and sometimes violence.
While the centrist candidate, who surrounds himself with Harvard and Oxford-educated advisers, has promised a renewed party, critics accuse him of 'old PRI' tactics, including an uncomfortably close relationship with Televisa, Mexico’s largest television channel.
He has vowed to shift the focus away from disrupting the cartels’ smuggling operations and look instead to curb the violence that all too often ends in beheadings or with bodies hung publicly from bridges.
He has promised to gradually withdraw the 40,000 soldiers deployed across the country, replacing them with a national gendarmerie tasked with bringing down violent crime.
