MEXICO CITY, Mexico (Reuters) - Mexico's old rulers were on track for a comeback as voters chose a new president on Sunday, after a grisly war with drug cartels and a sluggish economy wore down the ruling conservatives.
Twelve years after the Institutional Revolutionary Party (PRI) lost power, opinion polls showed its candidate, Enrique Pena Nieto, heading into the vote with a double-digit lead over his opponents.
Voters ousted the PRI in 2000 after 71 years of virtual single-party rule that was tainted by corruption, electoral fraud and authoritarianism.
But Pena Nieto has established himself as the new face of the party, which has bounced back, in part because of economic malaise and lawlessness under the conservative National Action Party (PAN).
A noisy crowd of protesters met Pena Nieto when he voted in Atlacomulco, about two hours northwest of the capital, but hundreds of his supporters shouted down the demonstrators.
A youthful-looking former governor of the State of Mexico, Pena Nieto promises reforms to improve the country's tax take, loosen the job market and open the state-owned oil firm Pemex to more foreign investment, citing Brazil's Petrobras as a model.
Mexicans are fiercely protective of Pemex, but the PRI, which nationalized oil production in 1938, could be the one party able to liberalize the energy sector.
"It's time for the PRI to return. They're the only ones who know how to govern," said Candelaria Puc, 70, preparing to vote in the beach resort of Cancun with the help of a friend because she cannot read or write.
"The PRI is tough, but they won't let the drug violence get out of control," she said in a mix of Mayan and Spanish.
Others feared a return to the worst years of PRI rule and put Pena Nieto's big lead down to his cozy relationship with Televisa, Mexico's top broadcaster.
"It's the same party as ever and the people who vote for him (Pena Nieto) believe they are going to live happily ever after like in the soap operas," Humberto Parra, a systems engineer, said as he went to vote in Mexico City.
Pena Nieto's closest challenger in pre-election polling was Andres Manuel Lopez Obrador, a leftist former Mexico City mayor often referred to by his initials AMLO, who narrowly lost the 2006 election to President Felipe Calderon of the PAN.
Exit polls from several regional elections also being held on Sunday showed the PRI was likely to capture the major western state of Jalisco from the PAN, and that the leftist Party of the Democratic Revolution (PRD) had kept control of Mexico City.
The PRI's allies, the Greens, were seen picking up the southern state of Chiapas from the PRD.
VIOLENCE HITS CONSERVATIVES
Lopez Obrador claimed fraud after the 2006 election and launched months of street protests that failed to overturn the result and instead alienated many former supporters. His claims that the PRI is this time planning fraud have raised concerns of more protests, although polls suggest Lopez Obrador will fall short of the 35 percent of votes he won in 2006.
"This is no time for the country to go in reverse," a relaxed Lopez Obrador said of the PRI before voting.
An official for the Federal Electoral Institute (IFE) said the election had probably registered the lowest number of complaints in Mexico's history.
But Lopez Obrador supporters stood ready to hit the streets if need be.
"We are with AMLO. I'm sure there will be fraud, and we will be ready to back him up if they steal the presidency," said Beatriz Sosa, 30, playing soccer with her six-year-old son in a park in the capital's upmarket Polanco neighborhood.
Bidding to become the country's first female president, PAN candidate Josefina Vazquez Mota was third in pre-election polls.
The PAN ended the PRI's long rule in 2000 but years of weak growth and the death of more than 55,000 people in drug-related killings since 2007 have steadily eroded its popularity.
Violence continued in the days before Sunday's vote.
In the Pacific beach resort of Acapulco, one of the cities most affected by the drug war, four people were killed on Saturday, two of them tortured and beheaded, a hallmark of drug-related killings.
The PRI mayoral candidate in the city of Marquelia, down the coast from Acapulco, was kidnapped for more than seven hours by an armed group, but released early on Sunday.
Final polls showed Pena Nieto winning 40 percent to 45 percent of the vote and Lopez Obrador close to 30 percent with Vazquez Mota not far behind. The candidate with the most votes wins, with no need for a second round.
The first national exit polls were expected when voting ends in the westernmost part of the country at 8 p.m. Mexico City time (2100 EDT/0100 GMT).
The PRI laid the foundations of the modern state with a nimble blend of politics and patronage that allowed it to appeal to labor unions and captains of industry at the same time.
Mexicans eventually tired of the one-party rule that stifled dissent, rewarded loyalists and allowed widespread corruption.
The era of old-time PRI bosses known as "dinosaurs" gave way to a more democratic era under the 1994-2000 presidency of Ernesto Zedillo, who instituted reforms that allowed opposition parties to compete in a fair vote and oust the PRI.
Voters also elect both houses of Congress on Sunday.
The legislative results will help determine whether Pena Nieto will be able to push through his reform agenda.
(Additional reporting by Dave Graham, Ioan Grillo, Gabriel Stargardter, Mica Rosenberg, Tomas Sarmiento, David Alire Garcia, Simon Gardner, Isela Serrano, Michael O'Boyle and Luis Enrique Martinez; Editing by Christophr Wilson and Daniel Trotta)