Updated

Rivals of the front-runner in Mexico's presidential race attacked him Sunday night as a liar with ties to corrupt figures in the country's former ruling party, filling the first candidates' debate with acrimonious exchanges of accusations and counter-accusations.

The tone heated up nearly halfway through the two-hour debate as Andres Manuel Lopez Obrador, the third-place candidate of the leftist Democratic Revolution Party, reached behind his lectern and pulled out a photo of Enrique Pena Nieto, the candidate of the Institutional Revolutionary Party, smiling alongside a political ally whose career ended in accusations of corruption.

"Who is Enrique Pena Nieto, really?" Lopez Obrador asked.

Pena Nieto pulled out his own photo of a former Lopez Obrador aide jailed on a corruption charge.

Minutes later, Lopez Obrador showed the camera another photo, of Pena Nieto with former President Carlos Salinas, whom Lopez Obrador painted as evidence of a clique of power-brokers trying to retake power for the party that ruled for 71 years before it lost the presidency in 2000.

Josefina Vazquez Mota of the ruling National Action Party, running nearly 20 points behind Pena Nieto in most polls ahead of the July 1 vote, leaped in with her own prop, a blown-up cover of an Economist magazine profile of Pena Nieto that she said showed that he had lied about reducing homicide figures during his term as governor of the state of Mexico.

"There are two ways of lying," she said. "One, not telling the truth and the other, making up statistics."

The first televised debate among the four presidential candidates was seen as a key opportunity for Pena Nieto's rivals to cut into his double-digit lead as he seeks to return the country's former ruling party to power. Observers said the debate would be a test of whether Pena Nieto, a telegenic former governor of Mexico state who is married to a Mexican soap opera star, could stray from his carefully choreographed campaign and think on his feet.

With questions agreed-upon beforehand, he stuck to his themes of change and competence, and parried Vazquez Mota's critiques as based upon incorrect information, a frequent refrain from his team in the first month of the campaign. Under more pointed attack from Lopez Obrador and Vazquez Mota, his responses grew more aggressive and heated, but he avoided any major errors in the first two-thirds of debate.

"They seem to have come to an agreement," he said, after a round of attacks from his two main opponents. "They're coming with knives sharpened."

Pena Nieto opened the debate by describing Mexico's economic performance as the worst in 80 years, saying "there aren't enough jobs, and the ones that exist don't pay well."

Vazquez Mota emphasized her role as the only woman in the race, and sought to de-emphasize her ties to the party that has governed for the last 12 years.

"I want to be president because I have the sensitivity, as a woman, to listen," she said. "I'm a different candidate ... different because I don't belong to powerful, privileged groups, because I'm honest."

Another presidential debate is scheduled for June 10.

Vazquez Mota went on the attack against the former governor's record minutes into the campaign, saying the state of Mexico had one of the country's worst economic records under his administration.

"It doesn't cease to surprise me that he talks about objectives that he was never able to achieve in the state of Mexico," she said.

Lopez Obrador portrayed both parties as bastions of an unjust socio-economic order in which billionaire businessmen enjoyed luxuries amid widespread poverty. Pena Nieto's rivals have argued that his party has not changed its autocratic and corrupt ways during its 12 years on the sidelines.

"This dominant group has privatized the government," Lopez Obrador said. "Do you think things will get better if the PRI comes back? Let's take a totally new path."

PRI strategists, in turn, were seeking to portray the party as one led by a new generation of politicians who will fulfill promises and not tolerate corruption.

"We recognize with clarity that this debate is going to be everyone against Pena" Nieto, Jorge Carlos Ramirez Marin, deputy coordinator of the PRI presidential campaign, told reporters on the eve of the debate.

Pena Nieto has been criticized for limiting his public exposure and canceling appearances at academic forums, part of a strategy of avoiding confrontations with his rivals.

Analysts say he has little to gain from such debates, and could only risk damaging his carefully managed image and hefty lead.

A survey by polling company Buendia & Laredo released Sunday in El Universal had Pena Nieto with 39.2 percent support, Vazquez Mota with 22.1 percent, Lopez Obrador with 17.5 percent and Gabriel Quadri of the New Alliance with 1.1 percent. The remaining people were undecided.

The poll surveyed 1,000 adults across Mexico and had a margin of error of plus or minus 3.5 percentage points.

Each candidate was given a question, and his or her rivals were allowed a chance to respond. The candidate was then given the opportunity for a counter-response. Some critics have said the format is too rigid to allow for a full debate.

The debate is being broadcast at the same time as the quarterfinals of a local soccer league, meaning the number of Mexicans watching the debate could be low.

___

E. Eduardo Castillo can be followed on Twitter at http://twitter.com/EECastilloA