With 11 states holding gubernatorial elections this year, the western state of Michoacan was seen as the PRD's best hope. Cuauhtemoc's father, Lazaro Cardenas, was governor of the state and one of the most popular presidents in the 1930s. When Cuauhtemoc unsuccessfully challenged Carlos Salinas for the presidency in 1988, he outpolled Mr Salinas there by nearly three to one. But on 12 July, the party lost its main stronghold to the ruling Institutional Revolutionary Party (PRI).
That result represents a dilemma for both parties. For the PRD, which has claimed widespread fraud at the polls, it will inevitably mean a shake-up of the party. For the PRI, desperate to prove that the government's days of stuffing ballot boxes are over, the problem is whether any decisive victory can be credible.
Mr Salinas won in 1988 in an election considered by many Mexicans to be fraudulent. Even official figures gave him only 50.4 per cent of the vote, the worst showing by a president in Mexican history. Since then, charges of vote-rigging have continued. 'We're paying the price for our past mistakes,' said Agustin Basave, a PRI congressman from the northern state of Nuevo Leon.
The PRI conceded defeat to the conservative National Action Party (PAN) in Chihuahua's gubernatorial election on 12 July - only the second time since the ruling party was founded in 1929 that an opposition candidate emerged victorious in a state election.
President Salinas is deeply aware of the need for political reform, and knows that with the Nafta free-trade pact pending, critics north of the Rio Grande are keeping a close eye on Mexico. Since coming to power, Mr Salinas has been obliged to remove eight state governors and he forced two PRI candidates from office last year after allegations of fraud in mid-term elections.
Party managers, headed by the PRI's new chief, Genaro Borrego Estrada, 41, are struggling to replace the traditional corporatist structure of the party with a regionally based organisation. They want to attract the new middle classes and have selected young professionals as candidates, rather than the politicos of the past. The 1988 shock convinced party leaders that the old PRI structure would have to change.
The PRI 'has to make reforms even deeper than those it has introduced already,' Mr Salinas told The Independent.
But the President believes political reform must follow economic consolidation. The demise of communism in the former Soviet Union has not gone unnoticed. 'We want a process of reform that lasts,' Mr Salinas said. 'And one that allows the country to keep itself together. Not reform that disintegrates the country, or that generates conflict.'
But a growing number of Mexicans question the wisdom of forging ahead with progressive economic policies while ignoring the cries for pluralism. For 63 years, Mexico's essentially one-party system has provided a stability envied throughout Latin America. With nine more state elections and dozens of municipal ones up for grabs, this year will be a test of how deep the government's commitment to democracy really runs.