Voters in Mexico exhausted by drug violence looked set Sunday to return to power the Institutional Revolutionary Party (PRI) with its charismatic new leader Enrique Pena Nieto at the helm. Crowds held back by metal fences cheered when the beaming candidate and Angelica Rivera, his telenovela star wife, emerged from their vehicle to vote in his hometown Atlacomulco, northwest of the capital.

"My wish is for the people to be the winners on this election day," said 45-year-old Pena Nieto, who posed for photos with his wife and the couple's six children before hugging and kissing well-wishers.

The center-left PRI used to be synonymous with the Mexican state as it governed for seven decades until 2000 through a mixture of patronage and selective repression -- isolating political foes through bought elections and skewed media coverage.

Current President Felipe Calderon's ruling right-wing National Action Party (PAN) has been hemorrhaging support due to the brutal drug violence that has killed over 50,000 people since he came to power in 2006.

His military crackdown on the cartels has turned parts of the country into war zones and despite presiding over a period of steady economic growth, Calderon leaves as an unpopular president with a dubious legacy.

The economy grew under Calderon, but so did poverty: 47 percent of Mexico's 112 million residents are poor, according to government figures.

Mexico is Latin America's second biggest economy after Brazil but there are nearly 15 million more poor people since the PRI left power, figures show. Poverty ranks second among voter concerns after insecurity.

Recent polls have shown Pena Nieto with a commanding lead over former Mexico City mayor Andres Manuel Lopez Obrador, from the leftist Party of the Democratic Revolution (PRD).

Josefina Vazquez Mota, a female former cabinet minister from Calderon's unpopular PAN party, trailed in third.

Lopez Obrador insists he can pull off an upset.

He ran for president in 2006 and lost to Calderon by less than one percent. He claimed that he had been robbed of victory and brought Mexico City to a virtual standstill with weeks of protests.

After casting his ballot in Mexico City, Lopez Obrador called on "all citizens to freely participate," saying "it's the only weapon citizens have for change."

Mexican presidents are elected by simple majority for six-year terms and are banned from running for re-election. There is no run-off vote.

Although mistrust in the electoral system runs high -- surveys suggest some 40 percent of the nearly 80 million eligible voters will not bother to show up at the polls -- some were keen to cast their vote.

"I've been here since 7 am to vote because it's probably the last time I can do it," said 86-year-old Maria del Pilar Amezcua, the first person to cast a ballot at her polling station in Mexico City's Huatulco neighborhood.

Election officials have worked hard to convince skeptics that the ballot will be clean but have faced a raft of complaints in the lead-up to the vote.

PAN accuse the PRI of handing out more than 9,900 gift cards to influence voters. Election officials pledged an investigation but refuse to freeze a bank account linked to the cards containing some $5.2 million.

The PRI has accused the PRD and PAN of attempting to sway voters by handing out bags of food and building materials. And the PRD, in turn, alleges "very serious irregularities" including PRI fuel charge cards.

Top election official Leonardo Valdes, however, insisted that this will be "the cleanest and most impartial" Mexican election ever. "Each vote will be scrupulously counted," he said.

Nearly one million Mexicans -- including election workers, volunteer citizens and party representatives -- as well as 700 international observers will be at polling stations overseeing the vote.

Also up for grabs are 500 seats in the Chamber of Deputies, where members serve for three years; 128 seats in the Senate, which has six-year terms; and various mayoralties and governorships.

Security is a top concern in Mexico. Kidnappings, drug hits and gang warfare have turned some areas into virtual war zones.

Extra army patrols were deployed in especially dangerous regions like the northern border town of Nuevo Laredo, where a car bomb -- a rarity in Mexico -- detonated Friday in front of the mayor's office.

The first exit polls will be made public when the polling stations close at 0100 GMT Monday. The first official results are expected at 0445 GMT.