MEXICO CITY (AP) — Furious at spiraling corruption and violence, Mexican voters unleashed a political earthquake Sunday by electing a leftist firebrand as president and giving him a broad mandate to overthrow the political establishment and govern for the poor.

A late-night official quick count from electoral authorities forecast that Andres Manuel Lopez Obrador would win with between 53 percent and 53.8 percent of the vote, a remarkable margin not seen in the country for many years. A prominent exit poll predicted that his party allies were poised to score huge wins in the Senate and lower house, possibly absolute majorities in both.

Lopez Obrador, who campaigned on vows to transform Mexico and oust the "mafia of power" ruling the country, rode widespread voter anger and discontent with the governing Institutional Revolution Party, or PRI, of President Enrique Pena Nieto and had led opinion polls since the beginning of the campaign.

The PRI, which dominated Mexican politics for nearly the entire 20th century and recaptured the presidency in 2012, was set to suffer heavy losses not just for the presidency but in down-ballot races as well.

In brief remarks at a hotel in central Mexico City, Lopez Obrador called for reconciliation after a polarizing campaign and promised profound change that respects the law and constitutional order.

"I confess that I have a legitimate ambition: I want to go down in history as a good president of Mexico," said Lopez Obrador, who won after losses in the previous two elections. "I desire with all my soul to raise the greatness of our country on high."

The president-in-waiting devoted much of his speech to appealing to citizens of all stripes and seeking to reassure those who have eyed his candidacy nervously.

"This new national project will seek to establish an authentic democracy and we do not intend to establish a dictatorship," Lopez Obrador said. "The changes will be profound, but in accordance with established order."

Conservative Ricardo Anaya of a right-left coalition and the PRI's Jose Antonio Meade acknowledged defeat shortly after polls closed nationwide. The quick count had them around 22 percent and 16 percent, respectively.

"The tendency favors Andres Manuel Lopez Obrador. ... I recognize his triumph," Anaya said in a speech to supporters.

"For the good of Mexico, I wish him the greatest success," Meade said minutes earlier.

Lopez Obrador supporters began wild celebrations in Mexico City, cruising up and down the central Paseo de la Reforma boulevard honking horns to the tune of "Viva Mexico!" and waving Mexican flags from car windows and moon roofs.

Thousands poured into the sprawling main square known as the Zocalo, where the 64-year-old former mayor had called on his backers to rally. Many danced to the trills of mariachi music.

Lopez Obrador spoke to the crowd there around midnight, saying to loud applause: "Today one stage has ended and we are going to begin another one — we are going to transform Mexico!"

Retired teacher Susana Zuniga beamed and said the country was experiencing a moment similar to the Mexican Revolution a century ago.

"The people are fed up," Zuniga said. "That is what brought us to this."

U.S. President Donald Trump tweeted congratulations: "I look very much forward to working with him. There is much to be done that will benefit both the United States and Mexico!"

Lopez Obrador said individual and property rights would be guaranteed, promised respect for the autonomy of the Bank of Mexico and said his government will maintain financial and fiscal discipline.

He said contracts obtained under energy reforms passed under President Enrique Pena Nieto will be scrutinized for any corruption or illegality, but otherwise contracts will be honored:

"There will be no confiscation or expropriation of assets. ... Eradicating corruption will be the principal mission," he said.

Lopez Obrador also spoke of support for migrants and said the most forgotten and humble people of Mexico will be given preference in his government. He said he will seek a relationship of "friendship and respect" with the United States. And rather than the use of force to fight spiraling violence, he will look to fix root causes such as inequality and poverty.