MEXICO CITY -- Enrique Pena Nieto, the president-elect of Mexico, will be forced to govern in a way that his once-autocratic Institutional Revolutionary Party isn’t accustomed to: by negotiating with political opponents.

Pena Nieto won 38 percent of the vote, with a 6 percentage-point margin over his nearest rival in Sunday’s election, a victory smaller than the one opinion polls had forecast and far from a resounding knockout, analysts said.

His modest triumph and the comeback of his party, known as the PRI in its Spanish initials, which has been out of power for the past 12 years, signaled that Mexicans wanted a new hand at the tiller to deal with soaring violence and modest economic growth that’s averaged about half the rate of other Latin American nations in recent years.

But a majority of voters cast ballots for someone other than Pena Nieto and denied the party a working majority in both chambers of Congress, meaning that the overhaul the 45-year-old former governor has proposed will come only through consensus with opposition parties.

“Voters fully expressed their distrust,” said Federico Estevez, a political scientist at the Mexico Autonomous Institute of Technology. “He’ll be hampered by the Senate for a full term.”

Pena Nieto made some 250 promises during the campaign, ranging from vast and profound structural revisions to throwaway pledges to appeal to various regions and voter groups. The deep restructuring includes changes to energy, labor and fiscal policies that would take an ax to some of the edifice of state that his party helped construct during the 1929-2000 period it ruled without interruption.

One of his pledges was to slash 32 seats from the 132-seat Senate and 100 seats from the 532-seat lower house, the Chamber of Deputies. Such a change would require a constitutional amendment, possible only if the PRI wins support from its political opposition.

Experts said the need for coalitions underscored the linchpin role in Congress that would be played by the National Action Party (PAN), which has been in power for 12 years but whose candidate trailed in third place in Sunday’s vote, and the leftist Party of the Democratic Revolution (PRD), which placed second.

With nearly 32 percent of the popular votes, the second-place finisher Sunday was Andres Manuel Lopez Obrador, an often-fiery orator of the PRD who has yet to concede.

“Today, the left is the second political electoral force in the country,” analyst Denise Dresser told the MVS radio network, adding that she hoped the PRD “leaves behind its self-absorption and its pain and assumes the very important role to which it corresponds.”

“It’s the moment of the Mexican left, and I hope it understands this,” she added.

Pena Nieto promised Monday to run an administration that’s “modern, open to criticism and ready to listen.” He pledged to create jobs and combat poverty, and reiterated a vow to fight criminal groups and to reduce kidnappings, murders and extortions.

He also repeated a promise to seek consensus to govern on behalf of all of Mexico’s 113 million citizens, a veiled recognition of his limited mandate.

Pena Nieto will need center-right PAN legislators to negotiate sensitive changes to the energy sector, such as opening the state-run oil company, Pemex, to private investment in exploration, production and refining. Strong nationalism in Mexico makes changes to Pemex nearly a third rail in politics.