Mexicans voted Sunday in an election that could put a leftist leader at the US doorstep or keep the Latin American country on the conservative track that has won Washington's praise.
The presidential election was seen as a neck-and-neck race between Harvard-educated conservative Felipe Calderon, of the ruling party, and former Mexico City mayor Andres Manuel Lopez Obrador, of the leftist Party of the Democratic Revolution (PRD.)
Third place in opinion polls went to Roberto Madrazo, the leader of the Institutional Revolutionary Party (PRI,) which ruled Mexico with an iron fist for 71 years before the historic 2000 electoral victory by Vicente Fox, of the National Action Party (PAN.)
The three parties were also waging a close race in the congressional election, but none of them appeared likely to win an outright majority in the House or the Senate.
The US administration is keeping a close eye on the election, evidently hoping to see a reversal of Latin America's leftward tide.
Analysts believe that while Mexico might edge away from Fox's tight embrace of its northern neighbour, none of the candidates could afford to significantly alter relations with the United States, by far Mexico's largest trading partner.
The Calderon campaign has capitalised on fears among Mexican business leaders, likening the former mayor to Venezuela's virulently anti-US President Hugo Chavez, and warning he would plunge the country into a ruinous economic crisis.
Analysts generally dismiss the comparison and say that while Lopez Obrador has little interest in foreign policy, he is not hostile to the United States.
But Eduardo Matias Lopez, 50, who fled Cuba 20 years ago and has since become a Mexican citizen, worried about the consequences of a possible Lopez Obrador victory. "I am afraid we could have a regime like that of Venezuela or Cuba," he said as he stood in line at Mexico City's historic downtown square to cast his ballot.
"I fled Cuba because of an authoritarian regime and I will flee again if there is a similar regime in Mexico."
Lopez Obrador, 52, angrily rejects suggestions his policies would be anything less than democratic, and insists that the reforms he plans would improve the lot of downtrodden.
"If Lopez Obrador wins, there will be social change. It won't be a radical change, but the situation will improve, particularly for the most needy," said physical therapist Margarita Grijalba, 50, who woke up before dawn to vote.
Lopez Obrador says he would finance major job-creating infrastructure projects and hand out financial aid to elderly and handicapped people, as he did when he was mayor from 2000 to 2005.
For his part, Calderon, 43, a staunchly conservative former energy minister, wants to encourage foreign investment, allow private partnerships in the state-run oil sector and slash corporate taxes in order to boost economic growth.
The economy was stagnant for much of Fox's government but has now picked up, with soaring oil prices helping fuel economic growth, which rose to 5.5 percent in the first quarter of the year.
Lopez Obrador insists the wealth is not trickling down to the millions of Mexicans who live on less than two dollars a day and who in many cases risk their lives by crossing the northern border illegally in search of the American dream.
Whoever wins the presidential vote will face formidable challenges in trying to fulfil campaign pledges of battling poverty, corruption, common crime and drug-fuelled violence, and getting the congressional support needed to pass reforms.