MEXICO CITY (AP) — Voters in Mexico's most populous state on Sunday could hand the ruling party a much-needed boost ahead of next year's presidential elections or a potentially devastating blow by throwing off its uninterrupted 88-year local rule.

Polls gave the ruling Institutional Revolutionary Party of President Enrique Pena Nieto a slight edge in the closing days of the Mexico State campaign, but the result will largely depend on which party can get its backers to vote and the possibility of party switching by voters whose priority is preventing a PRI victory.

A loss for the PRI's Alfredo Del Mazo would be a "huge hit," said Jose Antonio Crespo, a political analyst at Mexico's Center for Economic Research and Teaching. "It would lose one of the most important bastions in terms of image, in terms of enthusiasm among PRIists."

The only certainty is that if the PRI wins there will be allegations of fraud, he said.

The federal electoral prosecutor's office said it has received a sharp increase in complaints of alleged irregularities and residents of the state report parties offering them packages of staple goods. Local newspapers published photos of money cards bearing the PRI insignia allegedly being handed out to potential voters.

The party, which dominated Mexico for most of the 20th century, has been struggling with low approval ratings under Pena Nieto, putting its hold on national power at risk in next year's presidential race.

A state victory for the PRI's closest competitor, the leftist Morena party and schoolteacher-turned-politician Delfina Gomez, would boost party leader Andres Manuel Lopez Obrador's chances as he prepares to make a third run for the presidency in 2018.

With polls showing about two-thirds of voters back parties other than the PRI, divisions in that anti-PRI vote could be the ruling party's best shot at retaining power in the state, and perhaps nationally: No Mexican president has gotten more than half the vote in an election in nearly two decades.

Voters in the states of Coahuila and Nayarit also will choose new governors on Sunday, but Mexico State is the country's biggest electoral prize. With 11 million voters and substantial industry and influence in the sprawl around Mexico City, it can be key to a presidential campaign, giving the victor resources and a wealth of patronage jobs for backers.

Pena Nieto himself was its governor, as were the father and grandfather of Del Mazo, who is himself a distant cousin of the president — a fact often trumpeted by opponents hoping to capitalize on Pena Nieto's low popularity, which is dipping near single digits nationally.

The PRI held power in Mexico from 1929 until 2000, and Pena Nieto recaptured the presidency in 2012. While it remains the only truly national party in Mexico, it lost governorships last year in four states it had never lost before. And it faces problems in Mexico State that the PRI is hard pressed to blame on anyone else.

Nearly everyone has a story about being robbed on the buses that shuttle people to and from work in the capital. Its sprawling Mexico City suburbs — some of them chaotic cities of 1 million or more in their own right — are plagued by violence, especially against women. Just this week, authorities in Chalco found the burned bodies of a woman and two children in a grassy lot.

For Francisca Anaya, a 52-year-old unemployed project manager from Ecatepec, getting a handle on crime is the top priority.

"We need new people, people really committed to citizens, who really apply the law, who give justice to the missing and murdered women in Ecatepec," Anaya said. "The women of Ecatepec right now are defenseless. There is no one to protect us. At any moment they can kidnap, rape, disappear us."