MEXICO CITY  - 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 temporary 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 working the fences, hugging and kissing well-wishers.

The center-left PRI was synonymous with the 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.

Recent surveys have shown Pena Nieto with a commanding lead over leftist ex-Mexico City mayor Andres Manuel Lopez Obrador, who narrowly lost the 2006 presidential election to Calderon.

Final opinion polls on Wednesday showed Pena Nieto winning with an expected margin of victory of between 10 and 17 percentage points.

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

Lopez Obrador, from the leftist Party of the Democratic Revolution (PRD), insists that his figures show he can pull off an upset.

He only lost to Calderon in 2006 by less than one percent and, after he claimed that he had been robbed of victory, weeks of mass protests followed, bringing Mexico City to a virtual standstill.

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. Consecutive re-election is also banned in all other elected positions. There is no run-off vote.

Mistrust in the electoral system runs high in this largely Roman Catholic nation. Pre-vote surveys suggested that 40 percent of eligible voters will not bother to show up at the polls.

"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.

This will be "the cleanest and most impartial" election ever, vowed Leonardo Valdes, head of the independent Federal Electoral Institute (IFE) on Sunday. "Each vote will be scrupulously counted," he said.

Nearly one million Mexicans - including IFE 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 are rampant in many regions of the vast country. Drug hits are common and gang warfare has left a grisly trail of dismembered bodies.

Despite Calderon's unpopularity, particularly over his failed drug war, his would-be successors have only proposed minor policy modifications.

Extra army patrols were being deployed in dangerous regions on election day for voter safety.

There was a special focus on the northern border town of Nuevo Laredo, where a car bomb - still a rarity in Mexico - detonated Friday in front of the mayor's office, shattering windows and injuring some pedestrians.

Polling stations opened at 1300 GMT in the world's 11th most populous country, and the first exit surveys will be made public when the last polls close at 0100 GMT Monday. Nearly 80 million Mexicans are eligible to vote.

Election officials are expected to announce the first official results at 0445 GMT Monday. Final results are expected later in the week.