The prospect that Mexico could join other Latin American countries in turning to the left came a step closer last weekend, as Andres Manuel Lopez Obrador officially began his campaign for the presidency.
Mr Lopez Obrador will need support from outside Mexico City to win
Mr Lopez Obrador, the country's most popular politician and the current favourite in the race, stepped down as mayor of Mexico City to campaign ahead of next year's election.
He will join Santiago Creel, a member of President Vicente Fox's governing National Action Party (PAN) and a close ally of the president, who quit his post as interior minister last month to launch his own presidential bid.
Should Mr Lopez Obrador win, it will be the first time a left-winger has been chosen since Mexico introduced democratic reforms ahead of elections in 2000, Professor Sergio Aguayo, a leading scholar and commentator on human rights in Mexico, told the BBC World Service's Analysis programme.
"We are going to decide and we are going to elect, in a peaceful way, for the first time in our history, a leftist president," he said. "This is a new stage, this is a new moment."
Time of change
Mexico's political landscape was dominated by the Institutional Revolutionary Party, the PRI, which ruled without a break for 71 years until 2000.
Mr Lopez Obrador, a career politician, was a member of the PRI until he moved further to the left and joined the PRD - the Party of the Democratic Revolution.
He rose swiftly, and in 2000 became mayor of Mexico City - home to a quarter of the country's electorate.
Since then he has established a number of work schemes to help the most disadvantaged in the city. He has acquired a reputation for honesty and getting things done, and rises at six every day to appear on morning talk shows.
Santiago Creel of the governing PAN will fight Mr Lopez Obrador
Although Mr Fox, of the right-wing PAN, was welcomed in as president in 2000, under Mexican law the president can only serve one six-year term, meaning he must stand down in June next year - and Mr Lopez Obrador seems well-placed to replace him.
"He's paying attention to the poor people of Mexico City, and Mexico is a country full of poor people - more than 50% of the population are below the poverty line," Prof Aguayo said.
"So it has been enough for him to give grants to single mothers, to poor people, to those that have been left outside of development."
Word of Mr Lopez Obrador's policies has spread, and many sectors of the population believe he can offer a solution to their woes, says Prof Aguayo.
Arturo Valenzuela, professor of Latin American studies at Georgetown University in Washington and a former adviser to Bill Clinton, knows Mr Lopez Obrador personally and says he believes the Mexican people are looking to him as a "can do" leader.
"The perennial question pollsters ask is: 'Are you somebody that can do something for me?'" he said.
Thousands protested against Mr Lopez Obrador's suspension
"In that sense he's captured the imagination."
In April, however, Mr Lopez Obrador's path to high office suddenly looked uncertain after he was suspended following his being implicated in a land scandal.
The Mexican Congress voted to strip him of immunity from prosecution - which could have barred him from the race.
But in the furore, thousands of Mexicans turned out to protest in a show of support. His supporters argued the campaign against him was politically motivated.
In a dramatic climbdown, Mr Fox - worried that sending Mr Lopez Obrador to prison would make him a martyr - reinstated him.
Prof Aguayo said he believed this is a critical moment for the country.
"We are inaugurating our democracy, and Mr Fox, our president, was cheating on our leading candidate, and using dirty tactics and dirty politics to stop him," he added.
However, Mr Lopez Obrador is not without his critics.
The Mexican business community is concerned about his lavish spending on public services. Mexico City's books are in the red.
And if he is going to have a chance in the election, Mr Lopez Obrador will need to garner support from people who live outside the capital.
Prof Valenzuela points out that his party, the PRD, does not have a strong national following.
As a left-wing contender, questions are being asked about what kind of president Mr Lopez Obrador would make: whether he has the left-wing idealism of Brazil's President Lula, or takes a more populist approach, such as Venezuela's Hugo Chavez.
But Andrew Selee, director of the Mexico Institute at the Woodrow Wilson Center, said he would not be like either of them.
"Hugo Chavez came to power in a country where institutions were really weak... Mexico is a country of very strong political institutions.
"If Lopez Obrador is elected president he will probably be facing a congress dominated by the opposition - he is going to have to govern by building coalitions and alliances with people.
"On the other hand, he's not Lula - Lula comes out of a long tradition of a left-wing party built in opposition to military dictatorship... while Lopez Obrador came out of the PRI and moved to the left - [he's] much more pragmatic and less ideological."