Mexico’s oldest party has lost control of the country’s most populous and influential state, in an election result that could signal the end of a powerful network that has dominated politics in the region for almost a century. Alejandra del Moral Vela – the candidate for the incumbent Institutional Revolutionary Party (PRI) which has governed the state of Mexico (Edomex) uninterrupted since 1929 – was beaten by eight points on Sunday, despite claiming victory during the vote count. The winner, Delfina Gómez, a former school teacher and mayor, and a close ally of the populist president Andrés Manuel López Obrador, will be the first woman to govern the sprawling state of 17m people that wraps around Mexico City. It’s a huge blow for PRI, which had clung on to Edomex despite years of allegations of foul play – and despite losing every other state and the presidency in recent years. It marked an impressive victory for Morena, the party founded by López Obrador, also known as Amlo, less than a decade ago. Gómez had consistently led in the polls, but in recent weeks the PRI had claimed that Moral was closing the gap and had the momentum. Last week, the PRI was forced to defend its candidate after a joint investigation published by the Guardian revealed that at least $300m had been embezzled by the state government through dozens of contracts awarded to front and shell companies between 2018 and 2022. Some of those contracts involved the social development department while led by Moral, who cancelled the final day of campaign events after the story broke. Now, the future of the PRI is “uncertain” after Sunday’s defeat, and this setback could prove to be “insurmountable” when it comes to contesting the presidential elections next year, according to political analyst Gabriel Corona Armenta at the National Autonomous University of Mexico. “The results on Sunday should have happened in 1999, but the PRI has managed to stay in power 24 extra years using electoral tricks, negotiations and money.” The outgoing governor Alfredo del Mazo Maza secured a narrow victory in 2017 amid widespread allegations of fraud, following in the footsteps of his grandfather, father, uncle and cousin Enrique Pena Nieto, who served as president between 2012 and 2018. The family, which has governed Edomex for a total of 29 years, are key players in the Atlacomulco group, a shadowy tribe of political and business powerbrokers that for years dominated the state and the country. Moral represented an alliance between Mexico’s three oldest mainstream parties – the PRI, the National Action Party (Pan) and the Party of the Democratic Revolution (PRD) – which had hoped that together they could defeat Gómez and Morena. But voters signalled they were ready for change in the region, which is one of the most dangerous and unequal in Mexico. Voter turnout among the middle class, which the PRI had been counting on, was particularly low and its messaging – and political strategy – failed, according to Juan Carlos Villarreal Martínez, a political scientist at the Autonomous University of the State of Mexico and director of the Ceplan polling firm. “It’s the same strategy that has led them to lose more than 20 states since 2018,” said Villarreal, adding that the party would have to change political direction in order to stand a chance in the 2024 elections. It’s unclear how much will actually change under Gómez, who takes power in September, but the results demonstrate people’s desire for change, according to Lenin Martell, a media studies professor and commentator from the Autonomous University of the State of Mexico. “People were fed up with abuses, femicides, kidnapping, a bad health system, and they are tired of the Atlacomulco group’s power which manipulated citizens through the media and public institutions. People wanted real social programmes which help the most marginalized social groups … After more than 90 years, the PRI is finally gone from the state of Mexico.”