Even in recent months, despite a surge of politician killings, Lopez Obrador has ventured into drug-cartel strongholds rarely visited by Pena Nieto, such as Chilapa and Reynosa.
A new president has been elected there. These are all factors that point to a stalemate, said Moshe Lander, an economist at Concordia University. 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.
"Investors are being reassured by the speeches by Lopez Obrador", said Carlos Capistran, an economist at Bank of America Merrill Lynch.
Lopez Obrador, a former Mexico City mayor, was greeted with rapturous cheers by supporters in the capital's Zocalo central square around midnight, while friends celebrated in his tiny hometown of Tepetitan, in the poor southern state of Tabasco.
"He who fights for justice has nothing to fear", Lopez Obrador said after meeting with President Enrique Pena Nieto, who he said offered federal protection. "I told him a number of years ago when I saw him campaigning for a different race, frankly, a different year, a different race, I said he'll be someday he's going to be the President of Mexico".
Mr Trump was quick to congratulate the 64-year-old, who has charted a careful course of not antagonising his northern neighbour but vowing to put Mexico first. Investors have always been expecting a victory by Lopez Obrador, who held double-digit leads in polls for months.
Voters will expect him to put into concrete action his anti-corruption agenda, reign in rising killings and cartel violence that have stubbornly resisted the efforts of his two predecessors, and revive a sluggish economy that grew just 2.1 per cent past year.
Only time will tell if these two non-traditional candidates will be able to build a non-traditional partnership that benefits both countries.
And when he takes office in December, AMLO-as the president-elect is known-will have to please those who voted for him.
"Front-runner Andres Manuel Lopez Obrador voted early, saying 'today the people will decide between more of the same or a real change". But he's been frustratingly vague on how he'll go about it. "Given the lame-duck government in Mexico and the fact that any revised NAFTA would have to be considered in 2019 by the U.S. Congress elected in November, it would not surprise me if negotiations continue at a slow pace".
In the past, Lopez Obrador has offered criticism to the shift in U.S. stance on immigration and trade. Beyond that, Ross said it was unclear whether Mexico's incoming president would either bring in new negotiators or set a different agenda.
However, opponents of Mr Lopez Obrador say he could turn Mexico into another Venezuela - where the authoritarian left-wing governments of Hugo Chavez and his successor Nicolas Maduro wrecked the economy and fostered corruption and political violence.
But the main question in the new era of AMLO and his party, Morena, will be whether Mexico-U.S. border security and anti-narcotics cooperation will maintain the close cooperation established over the past 12 years.
"We've been very nice to Canada for many years and they've taken advantage of that", Sanders said during her daily press briefing in Washington.