Enrique Pena Nieto delivered a stunning return to power for Mexico's once-reviled PRI party, but the president-elect faces a stiff challenge in cutting poverty and clamping down on rampant drug violence.
Pena Nieto, the telegenic fresh new face of the Institutional Revolutionary Party (PRI), declared victory in the presidential vote after first official results late Sunday showed him with 38 percent of the vote, ending more than a decade in the political wilderness for the PRI.
Leftist Andres Manuel Lopez Obrador from the Party of the Democratic Revolution (PRD) took second with 31 percent but refused to concede, claiming to have data showing different results.
The PRI was synonymous with the Mexican state as it governed for seven decades until 2000 using a mixture of patronage, selective repression, rigged elections and bribery.
"If these results are confirmed... Pena Nieto will be named president elect, and starting December 1, will be the next president of the republic," President Felipe Calderon said just after the first official results were out.
Calderon's ruling right-wing National Action Party (PAN) was third, losing support due to the brutal drug war that has claimed more than 50,000 lives since he came to power in 2006.
"I assume the mandate that Mexicans have given me," Pena Nieto said in his late Sunday victory speech, emphasizing that the country voted for a "change of course" and called for "the unity of all Mexicans."
On Monday, Pena Nieto, 45, tried to reassure the public that his election did not mean a return of the bad old days of the PRI.
"There is no return to the past. This PRI that is coming into office has proven its democratic conviction," he told a group of foreign reporters.
The president-elect also said he will maintain Calderon's strategy of using the military to attack the drug cartels and capture crime capos, but will focus on bringing down crime.
"Society clearly expects immediate short-term results ... like lower crime and kidnapping rates," Pena Nieto said.
An ex-governor of populous Mexico state, just west of the capital, Pena Nieto is married to glamorous soap opera star Angelica Rivera and benefited from family connections with powerful old guard PRI politicos, as well as a savvy media team that carefully stage-managed his appearances.
Leonardo Valdes, head of the independent Federal Electoral Institute (IFE), said the first official results late Sunday were based on returns from 7,500 polling stations and have a 0.5 percent margin of error.
In 2006, when Lopez Obrador ran for president and lost by less than one percent, he cried foul and organized protests that paralyzed Mexico City for more than a month.
Far behind in the initial results was Josefina Vazquez Mota from Calderon's PAN party with 25 percent, feeling the backlash from the incumbent's failure to smash the drug cartels.
PAN party head Gustavo Madero on Monday acknowledged the debacle, which included losing the governor's mansions in key states like their stronghold of Jalisco. "It was a capital defeat," he told local media.
Calderon's military crackdown has turned parts of the country into war zones and despite presiding over a period of steady economic growth, he leaves as an unpopular president with a dubious legacy.
The economy grew under Calderon, but so did poverty: 47 percent of 112 million Mexicans are poor, according to figures from the government, Latin America's second biggest economy, closely tied to those of the United States and Canada in the North American Free Trade Agreement (NAFTA).
Pena Nieto has promised public works like roads and bridges to increase employment.
Election officials worked hard to convince skeptics that the ballot would be clean but faced a raft of complaints in the lead-up to the vote.
The head of an observer team from a regional bloc, the Organization of American States (OAS), congratulated Mexico for the "calm, respect and order that prevailed" in Sunday's vote.
"Mexico enjoys today a robust and trustworthy electoral system, with an important amount of control that... should show the reliability of the electoral system," said the lead observer, former Colombian president Cesar Gaviria.
Media projections indicate that the PRI will have a majority in both chambers of Congress. In the Senate, the PAN has the second largest number of legislators, while the PRD is second in the chamber of deputies.