MEXICO CITY -- Mexico's presidential election was too close to call Sunday, with a leftist offering himself as a savior to the poor and a conservative free-trader both declaring themselves the winner. Officials said they won't know who won for days.

Electoral officials said they could not release the results of Sunday night's quick count of the votes, which they previously said would happen only if the leading candidates were within one percentage point of each other. Luis Carlos Ugalde, president of the Federal Electoral Institute, said an official count would begin Wednesday, and a winner will be declared once it's complete.

Felipe Calderon, 43, of outgoing President Vicente Fox's National Action Party, had been running an exceedingly close race with Andres Manuel Lopez Obrador, 52, of the leftist Democratic Revolution Party. The Institutional Revolutionary Party's Roberto Madrazo, 53, had been trailing in third place.

Fox appealed for calm amid fears that a close result would raise the potential for violence.

Thousands of Lopez Obrador supporters, waiting for hours in the cold rain in Mexico City's central plaza, began shouting "Fraud! Fraud!" when Ugalde came on live television to announce the delay. Lopez Obrador said late Sunday that he would respect the delay in declaring a winner, "but I want the Mexican people to know that our figures show we won."

Calderon spoke minutes later, saying he too will respect the results -- but that the official preliminary results, as well as the exit polls, show that he's the winner.

"We have no doubt that we have won," he said.

The race exposed deep divisions between Mexico's rich and poor in a nation desperately trying to match the success of its northern neighbor.

The vote was the first since Fox's stunning victory six years ago ended 71 years of rule by the Institutional Revolutionary Party, or PRI, and it could determine whether Mexico becomes the latest Latin American country to move to the left.

Electoral officials said voting was relatively peaceful, although many voters complained polls opened late or ran out of ballots.

Luis Carlos Ugalde, president of Mexico's Federal Electoral Institute, said only eight of more than 130,488 polling stations failed to open -- the fewest in Mexico's history.

"We've had an exemplary election day, of which all Mexicans can be proud," Ugalde said.

Exit polls indicated National Action Party did well in three governors races -- Morelos, Guanajuato and Jalisco -- while Marcelo Ebrard of Lopez Obrador's party won the Mexico City mayor's post.

As for Congress -- key to determining whether the next president will be able to push through reforms -- none of the parties dominated. Two exit polls, both with a 1.5 percent margin of error, gave National Action 35 percent, Democratic Revolution 31 percent and the PRI 28 percent of the lower house of Congress.

In the past, Lopez Obrador has not hesitated to mobilize millions to get his way. As Mexico City mayor, he successfully persuaded the Fox administration to drop charges against him by staging massive protests, and he refused to accept his loss to Madrazo in a 1994 gubernatorial race.

A drawn-out period of uncertainty could rock financial markets and unsettle Mexico's maturing democracy.

In Guerrero state, two poll workers were shot to death before the polls opened, according to Lopez Obrador's party. Electoral officials said they were investigating, but the killings appeared unrelated to the vote.

Many polling stations opened late, forcing voters to wait more than an hour to cast their ballots. Carolina Nougue, 35, a perfume factory manager, sat angry outside a polling station tucked between two massive shopping malls in an upscale Mexico City neighborhood.

Nougue said she was reluctantly casting her vote for Calderon to keep Lopez Obrador out of office. She described herself as leftist but worried that Lopez Obrador would govern like radical Venezuelan President Hugo Chavez, and was turned off by his pledge to put the poor first.

"The division isn't between the rich and the poor," she said. "It's between the ignorant people and those who think."

In Nezahualcoyotl, a slum of 1.2 million people east of Mexico City where infrastructure has not kept up with explosive growth, voting was delayed by flooding from a powerful hail storm the night before. Juana Velasquez, 63, and other residents had to spend the morning bailing water from their homes.

"Every year, it's the same. You just vote for someone who doesn't do anything," said Velasquez, who cast a protest vote for Roberto Campa of the minor New Alliance Party.

Some simply refused to take part.

"We aren't going to vote," said Maria del Carmen, a 24-year-old student marching down Mexico City's Reforma Avenue with Zapatista rebel leader Subcomandante Marcos and hundreds of supporters. "We don't believe in the system and we are going to show our strength."

Early riser Lopez Obrador, dressed in a brown leather jacket, was the first candidate to cast his ballot, and had to wait nearly an hour before volunteers were ready.

"We did our part," he said.

During his campaign, he accused Calderon of catering to the rich and promised he would govern for Mexico's 50 million poor. Many followed his message like a religion, crowning him with flowers at rallies and plastering their cars with his optimistic slogan: "Smile. We are going to win."

Calderon has warned that Lopez Obrador's proposals, including government handouts for the elderly and poor, will bankrupt the nation.

Wearing a suit and tie, he showed his right palm before voting in Mexico City, a reference to his "clean hands" campaign slogan.

"It has been a tense, competitive campaign," he said, adding: "Tomorrow, we have to start a new era of reconciliation."

Mexican law limits presidents to one term, and provides for an unusually long handover of power. Fox will remain in office until December, then retire to his ranch.

On Sunday, which happened to be his 64th birthday, Fox gave an ink-stained thumbs-up to prove he voted and said: "I know that there are no Mexicans who want to go against democracy."

About 71 million of Mexico's 103 million people were eligible to vote.

The estimated 11 million Mexicans living in the United States were allowed to vote from abroad for the first time, but the 32,632 ballots they cast weren't likely to make much of a difference.

Thousands who missed out on the new mail-in vote -- including farm workers and construction laborers living in California -- traveled to Mexican border cities on Sunday to cast their ballots at polling stations.

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Associated Press writers contributing to this report are Mark Stevenson, Will Weissert, Istra Pacheco and Kara Andrade in Mexico City; Ioan Grillo in Villahermosa, Mexico; and Olga R. Rodriguez in Tijuana.