MEXICO CITY -- Hours after voters returned his former ruling party to power, Enrique Pena Nieto thanked Mexicans for offering a "second chance" and promised to abandon the party’s autocratic ways and preside over a modern, inclusive administration.

“We are a new generation. There is no return to the past,” the 45-year-old former governor pledged in a victory speech at the headquarters of his Institutional Revolutionary Party.

Pena Nieto declared that he “understands the changes that the country has experienced in recent decades, and will act according to the new reality.”

“I will pursue a modern presidency,” he added, “responsible, open to criticism, willing to listen and take account of all.”

With 81 percent of voting precinct tallies counted, Pena Nieto led with 37.4 percent of votes, followed by Andres Manuel Lopez Obrador of the leftist Party of the Democratic Revolution with 32.4 percent.

Trailing behind were Josefina Vazquez Mota of the ruling center-right National Action Party (PAN) with 25.4 percent and a fourth candidate, Gabriel Quadri de la Torre of the New Alliance with barely over 2 percent.

President Felipe Calderon, whose PAN lost badly in Sunday’s vote after 12 years of rule, promised an “orderly, transparent and efficient” transition.

“I want to sincerely congratulate him,” Calderon said of Pena Nieto.

Lopez Obrador declined to concede the triumph to Pena Nieto, a boyish-looking 45-year-old married to a television soap opera star. He said he would await “all the results” before speaking further.

Many Mexicans voted in a sour mood over drug-war violence and an economy only recently gaining steam. They were ready to give a new chance to a party that ruled from 1929 until 2000, casting aside concerns over its autocratic past.

Scattered irregularities were reported at a few of the nation’s 143,000 voting stations, but for the most part the vote appeared calm and orderly.

In a closely watched race in the capital, exit polls gave a landslide victory to the Party of the Democratic Revolution’s Miguel Angel Mancera, allowing the party to hang on to Mexico City Hall, which it has controlled for a decade and a half.

It is an election that has been closely watched in the United States. Not only does the United States share a nearly 2,000 mile border with Mexico, but the two countries have key mutual interests in areas such as trade, energy, homeland security and migration. Mexico is the third largest U.S. trading partner (after China and Canada) and also a vital source of crude oil to U.S. markets.

As many as six million U.S. jobs depend on trade with Mexico and 10 million U.S. citizens visit Mexico every year. Increasingly, criminal gangs in Mexico have tentacles that reach into U.S. cities.

The return of the PRI, as the party is known because of its Spanish initials, amounted to an about-face for Mexico.

Mexicans fought for decades to topple the PRI from its 71-year grip on power, eventually ousting the party in 2000.

Some critics say a triumph of the PRI would lurch Mexico backward to its authoritarian past. Supporters say the PRI has learned from its past and won’t rule as it once did, even if some within its ranks do not embrace the change.

The party would face opposition in Congress, a robust media, a largely independent Supreme Court and strengthened civil society groups that employ social media tools aggressively.