Preliminary results show voters in Mexico have chosen to bring the country's once dominant political party back into power by electing Enrique Pena Nieto as their next president.
Election officials said late Sunday that Pena Nieto had 38 percent of the vote to beat former Mexico City mayor Andres Manuel Lopez Obrador, who had 31 percent.
Lopez Obrador said he was not ready to concede.
Pena Nieto's Institutional Revolutionary Party ruled Mexico for 71 years until 2000, when voters elected National Action Party (PAN) candidate Vicente Fox. Outgoing President Felipe Calderon, also from PAN, followed in 2006, but his tenure has been plagued by economic stagnation and rampant drug violence.
Mr. Calderon deployed the military to fight the drug cartels shortly after he took office. More than 50,000 people have been killed in drug violence since then.
Pena Nieto said in an address to his supporters that Mexicans have voted for a change in direction, but he vowed to keep pressure on the cartels.