A voter survey for newspaper El Universal after Sunday night's debate showed 36.3 percent backed Pena Nieto of the opposition Institutional Revolutionary Party (PRI) as president, a lead of nearly 13 points over his nearest rival.

Second placed in the telephone survey by consultancy Loger Consultores was leftist challenger Andres Manuel Lopez Obrador, who received around 23.4 percent of voters' backing after a combative performance during the exchanges.

The respondents said they felt the 2006 presidential runner-up beat Josefina Vazquez Mota of President Felipe Calderon's conservative National Action Party (PAN), who has been ahead of Lopez Obrador in most polls. She received 22 percent backing.

Lopez Obrador and Vazquez Mota took turns to attack Pena Nieto for his record as governor of the State of Mexico, accusing him of corruption and incompetence in the two hour debate, though the PRI hopeful returned fire.

Pena Nieto ran Mexico's most populous state between 2005 and 2011 and the poll showed 31.6 percent of voters felt the youthful 45-year-old had won the debate, compared with 20.8 percent for Lopez Obrador and 17.3 percent for Vazquez Mota.

According to the survey, the biggest winner of the night was a fourth candidate, Gabriel Quadri of the New Alliance Party, a small group with strong ties to the powerful teachers' union.

Surveys have shown Quadri winning just 1 percent to 2 percent of the presidential vote, and he was ignored by the others, enabling him to talk freely and make light of the three main contenders.

More than 18 percent of those polled for El Universal said Quadri, frequently dismissed by critics as a puppet of teachers' union boss Elba Esther Gordillo, won the debate and nearly 10 percent said they would vote for him afterwards.

Exchanges between the candidates focused on how to lift the economy and curb the drug-related violence racking Mexico, which has claimed more than 50,000 lives over the past five years, damaging support for Calderon's PAN. The constitution prevents Calderon from seeking a second term in office.

The poll had a sample size of 2,100 voters and a margin of error of 2.14 percentage points, the newspaper said.

(Reporting By Dave Graham)