After five nightmare months, including an Indian guerrilla uprising, the murder of the original PRI presidential candidate and the kidnapping of two of the country's wealthiest businessmen, matters have changed.
From appearing a rock of stability, poised to make the symbolic leap across the Rio Grande from the Third World to an industrial power on the back of a free trade agreement with the United States and Canada, Mexico has slid back towards the status of banana republic.
The few hundred thousand wealthy families, who control 95 per cent of the country's wealth, began to switch money from pesos to safe-haven dollar accounts across the border in San Diego, El Paso, Brownsville and Miami. Mexican banks upped their interest rates to attract them back.
Not least because of the January Indian rebellion, whose charismatic leader, 'Marcos', threatens to launch a new rising if August's presidential elections are not free and fair, Mr Zedillo felt obliged to face his opponents.
It was a gamble he neither lost nor won. Democracy, an over-used word but under-employed practice in Mexico, was perhaps the real winner of the historic debate.
About 30 million people, or 37 per cent of the population, watched Thursday night's 90-minute television show at home. Several hundred turned it into a fiesta. They gathered to watch the programme on a giant screen, below the gilt Angel of Independence monument, on Mexico City's Reforma boulevard.
Mr Zedillo, 42, who was named the PRI presidential candidate after Luis Donaldo Colosio was shot in the head by a young assassin while campaigning in the border city of Tijuana on 23 March, held his own.
He avoided over-reacting to his opponents' assaults. As a result, it was generally agreed that he had not harmed his chances. Partly because free choice is a novelty in the country, partly because of the PRI's Soviet-like grip on society, polls show him way ahead, with a projected 58 per cent of votes.
They suggest that Cuauhtemoc Cardenas, 60, who defected from the PRI in 1987, and whose father, Lazaro Cardenas, was a former president of Mexico, will win 22 per cent of the vote.
The third leading candidate, Diego Fernandez de Cevallos, of the conservative, business-orientated National Action Party (PAN), is projected to win around 15 per cent.
The figures are misleading. The 40 million Mexicans who live in poverty - half the population - also live in fear of the ruling party, and of party-controlled unions and landowners. They are not likely to say anything against the PRI in public. Their votes have long been guaranteed by party pressure. In the countryside, this is often represented by so-called 'white guards' or PRI-backed gunmen. The practice of ballot box-stuffing remains widespread.
Mr Zedillo remarked in the debate that 'the first hurdle we will have to overcome is extreme poverty'. This rang hollow from one of the white elite, among the nation's vast majority of Indians or poor mestizos (mixed race).
Mr Cardenas concentrated on the fact that he still believes he won the 1988 race against Carlos Salinas de Gortari, but was robbed through fraud. Many Mexicans, even those who will vote PRI or PAN, for fear of Mr Cardenas's populist policies, agree that the last election result was rigged.
Mr Fernandez de Cevallos, 53, whose party, PAN, has made strong inroads across the wealthier north, was widely agreed to have improved his chances with his performance. He noted with irony that Mr Zedillo had been named by the PRI to replace Mr Colosio by the dedazo (big finger) system - appointed arbitrarily, without a vote. Since Mr Colosio received the original 'big finger', Mr Zedillo is jokingly referred to by many Mexicans as 'Dedillo' (little finger).
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