At stake is the legacy of Rafael Correa and his decade-long leftist rule. The future of WikiLeaks founder Julian Assange is also at stake, as one candidate has vowed to boot him from their embassy in London.
Voters in Ecuador are going to the polls Sunday to decide if the country will maintain its left-of-center political path, or jump tracks to the right.
The run-off election features Lenin Moreno as heir to Rafael Correa's decade-long left-wing rule, which saw the country's poverty rate plunge from 37 percent to 23 percent. He is facing off against the conservative former banker Guillermo Lasso.
Moreno, representing the ruling PAIS alliance, won 39.36 percent of the vote in the election's first round in February, falling just short of the 40 percent and 10-point-lead necessary to win outright.
Lasso won 28.9 percent of the first round's votes, but right-wing voters are expected coalesce around him after conservative Congresswoman Cynthia Viteri, who finished third in the first round, threw her support to him.
Correa won a loyal following among Ecuador's poor with generous social benefits that dramatically reduced the poverty rate in the country of 16 million people.
But he has also faced accusations of corruption and squandering the windfall of the oil boom.
Political analyst Napoleon Saltos of the Central University of Ecuador said the election would come down to "the vote against the government and the fear among certain parts of the population that they will lose what they gained over the past 10 years."
Moreno has an edge
Polls give Moreno an edge heading into the runoff, with between 52.1 percent and 57.6 percent of the vote. Should Ecuador maintain a left-of-center trajectory, it would buck a regional trend.
Argentina, Brazil and Peru have all lurched to the right in recent months, as the region has drifted into recession and leftist leaders have been tarnished by a string of corruption scandals.
For years Ecuador's oil-rich economy benefitted from the high prices of crude. The economy generated solid economic growth of 4.4 percent per year on average during the first eight years of Correa's presidency, before tipping into recession in mid-2015.
The 61-year-old Lasso is director of the country's largest bank, Banco de Guayaquil. He previously served as finance minister, provincial governor and US ambassador in the government of former president Yamil Mahud.
Moreno, 64, was Correa's vice president until 2013, when he became the United Nations special envoy on disability. The author and former professor uses a wheelchair after a shooting in 1998 left him paraplegic.
The election could also decide the fate of WikiLeaks founder Julian Assange, who has been holed up at the country's London embassy since 2012. Lasso has vowed to expel Assange from the embassy if he is elected.
Assange sought sanctuary in the diplomatic mission to avoid sexual assault charges in Sweden, and possibly more serious charges in the United States.
Polls opened at 7:00 am (1200 GMT).
bik/rc (AFP, dpa)