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Mexico's Institutional Revolutionary Party was headed toward a decisive win in voting for governor of the country's most populous state, according to exit polls, a result that would boost the party's chances of retaking the presidency in national elections next year.

Two exit polls showed PRI candidate Eruviel Avila winning in the state of Mexico with 64 percent and 60 percent support respectively. Polls showed PRI candidates also winning elections in the states of Coahuila and Nayarit.

A PRI victory in all three states had been widely expected, with observers closely watching the margin of victory for signs the PRI is gaining or losing momentum headings into national elections.

Avila went into Sunday's vote with a 30-point lead for the PRI, which has never lost the governorship of Mexico state in more than 80 years.

Mexico state is the country's most populous, home to 15 million people and the sprawling, impoverished suburbs that ring Mexico City.

This year's vote in the state is especially crucial because the current PRI governor is Mexico's early presidential front-runner. Many will see Sunday's vote result as a reflection of the popularity of soon-to-be-outgoing Gov. Enrique Pena Nieto and a landslide will strengthen the telegenic candidate's chances in 2012 elections.

The private poll by Mendoza Blanco y Asociados, carried out for TV Azteca, has Avila with 64 percent support, Alejandro Encinas of the Democratic Revolution Party, or PRD, with 23 percent and Luis Felipe Bravo Mena of President Felipe Calderon's National Action Party with 13 percent.

The poll showed the PRI also winning in Coahuila state with 65 percent support and in Nayarit with 48 percent. The poll had a margin for error of 4 percentage points.

A second poll by the firm Mitofsky, conducted for the Televisa network, has Avila with 60 percent support, following by Encinas with 28 percent and Bravo Mena with 12 percent. The poll did not provide of margin of error.

The PRD and PAN, trailing in the polls and lacking the coalitions that have defeated the PRI in other states, warned voters that backing the PRI is backing a return to the past, when the "dinosaurs" wielded power through coercion, corruption and intimidation. The PRI governed Mexico for 71 uninterrupted years until losing presidential elections in 2000.

Election day had a bumpy start for some: Flooding caused by days of heavy rain forced officials to relocate more than 170 voting booths in two of the state's largest cities, said Fabiola Bueno, a spokeswoman for the state's electoral institute.

The relocation has affected more than 47,000 registered voters in Ecatepec and Nezahualcoyotl, just outside Mexico City, Bueno said. Tropical Storm Arlene dumped heavy rains on both cities Thursday, causing a river that carries sewage to overflow into residents' homes.

Accompanied by his two children, Avila cast his vote in Ecatapec, the most populous city in the state where he served as mayor before becoming a gubernatorial candidate. Aside from the flooding, the candidate said he expected a largely peaceful and trouble-free election day.

"I'm confident that today will be a fiesta for democracy," he said.

Avila has not commented in recent days on the potential impact the Mexico state election could have on the PRI's efforts to retake the presidency.

Asked Sunday whether the elections could give the PRI a boost ahead of 2012, Avila responded: "I'll answer that when this election ends."

The PAN and PRD tried early on to form a coalition to defeat the PRI, as they did last year to win the PRI stronghold states of Oaxaca, Puebla and Sinaloa. But the agreement fell apart in Mexico state, and other coalition efforts never got off the ground in Nayarit and Coahuila.

Across Mexico, many voters are weary of the PAN, which after more than a decade in power has failed to make fundamental changes in Mexico apart from a trademark war on organized crime that has seen a spike in violence. Since Calderon took office in late 2006, more than 35,000 people have died in drug violence, according to the government. Other sources put the number at more than 40,000.

And internal fighting in the PRD has left the leftist party in disarray.

The PRI has sprung back in the vacuum.

Euralia Contreras, 66, who voted at the same station as Avila, said that she was sure the PRI would win because it has tackled local problems and helped residents. "I've received many benefits from (Avila)," Contreras said, referring to free canned foods the Avila campaign gave her. "The handouts came through. He has fulfilled his promises."

After mounting one of the most expensive campaigns in Mexico's history, Avila ran tirelessly as a "democrat," polling near 60 percent while Encinas' support has hovered in the mid-to-high 20s in surveys by the newspapers Reforma and El Universal. Those polls have a margin of error of plus or minus 3 percentage points.

The newspaper Reforma reported last month that Avila's campaign spent nearly 4.4 million pesos a day ($376,000), more than the 3.4 million pesos ($290,000) Calderon spent to win the presidency. The campaign didn't respond to questions about spending from the AP.

For Fernando Pasillas Villarreal, there are no good candidates.

"I'll vote, but only to cancel my vote, because I think that although the governor may change, the one who takes his place does not offer substantial improvements, and I still think that the PRI only enriches itself and enriches its friends."

Even as the opposing parties cry foul and have filed complaints with the national elections tribunal over alleged PRI campaign violations, the elections Sunday and next year appear to be the PRI's to lose.

In the state capital of Toluca, where initial election results were expected to be announced Sunday evening, people turned out early to vote.

"Although none of the three candidates convinces me ... perhaps the only one who really knows Mexico state is from the PRI, Eruviel," said Leticia Aguilar Hernandez, a 50-year-old secretary.

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Associated Press writer Gloria Perez in Toluca, Mexico, contributed to this report.