By Dave Graham

MEXICO CITY Mexicans began voting in a state election on Sunday that looks poised to bolster President Andres Manuel Lopez Obrador ahead of the race to succeed him, with his party forecast to capture the chief remaining bastion of the country's old rulers.

Lopez Obrador's leftist National Regeneration Movement (MORENA) is expected to tighten its grip on power by adding the governorship of the State of Mexico to the 21 regional governments it already controls, two-thirds of the total.

The most populous region of the country, the State of Mexico surrounds much of the capital and has been an economic and electoral bulwark of the centrist Institutional Revolutionary Party (PRI), which has governed there since 1929.

Lopez Obrador routed the PRI to win the presidency in 2018, and MORENA has since absorbed most of the once-dominant party's strongholds, as well as many of its politicians.

The voting on Sunday comes a year before Mexico's next presidential election, with polls indicating MORENA will be very hard to beat then, too.

Decades of one-party rule made the PRI a byword for corruption among many Mexicans, and it has struggled to compete with MORENA's message that it represents a vote for change.

A poll published by newspaper Reforma showed the gubernatorial race has narrowed, but still gave MORENA's candidate Delfina Gomez a 10 percentage point lead over Alejandra del Moral, a PRI politician fronting an opposition alliance.

"People are leaning toward Delfina because she seems like a new start, as with Lopez Obrador," said Jose Hernandez, a 64-year-old shopkeeper in Los Reyes Acaquilpan, a town in the eastern part of the state of 17 million people. "Because, in short, the whole of (the PRI) has been corrupt."

Polling stations opened at 8 a.m (1400 GMT) and are set to close at 6 p.m. (0000 GMT). The State of Mexico's electoral body is due to begin publishing results an hour later as they come in.

Gomez is vowing to give a fresh start to the state and to improve security, mindful of widespread concern over violence. Del Moral has said the PRI learned from its mistakes and that her coalition will be a broader alternative to MORENA.

In a separate election on Sunday, the PRI is forecast to maintain the northern border state of Coahuila, where splits inside MORENA produced rival left-wing candidates. MORENA has sought to consolidate support in Coahuila by pressuring one of its national allies to abandon the renegade contender.

PRESIDENCY RACE

Lopez Obrador has dominated political life since taking office in December 2018, and his popularity, holding firm around 60%, has helped make MORENA a formidable electoral machine. Under Mexican law, presidents may serve only one six-year term.

Nevertheless, his abrasive style and uncompromising agenda, which has pitted the state against private enterprise, and fueled conflict with curbs on that power such as the judiciary, have polarized voters. Lopez Obrador has frequently criticized some sectors of middle class voters, and Mexico City and the State of Mexico in 2021 dealt MORENA unexpected setbacks in local elections.

Mexico City's mayor, Claudia Sheinbaum, has had a slight edge in most polling for the race to be MORENA's presidential candidate, pressed hard by Foreign Minister Marcelo Ebrard.

Sheinbaum, like Gomez, MORENA's State of Mexico candidate, is closely identified with Lopez Obrador and his agenda.

Failure to capture the State of Mexico, some analysts argue, could help make the case for putting up a presidential candidate with more moderate credentials such as Ebrard.

Because a MORENA victory has been taken for granted for months, an upset would give a powerful boost to the opposition, said Roy Campos, head of polling firm Consulta Mitofsky.

"For MORENA to lose this state," Campos said, "would basically mean getting off to a really bad start for the contest in 2024."

(Reporting by Dave Graham; Editing by Aurora Ellis and Will Dunham)