“We are going to defend the will of the Ecuadoran people in the face of an attempted fraud that aims to install what would be an illegitimate government,” he said, setting up what could be a long and ugly fight.

The election is being closely watched as a barometer of the political climate in Latin America, where more than a decade of leftist dominance has been waning.

It may also decide the fate of WikiLeaks founder Julian Assange, who has been holed up in Ecuador’s London embassy since 2012.

Both candidates claimed victory on the basis of conflicting exit polls.

“We will continue this process that has changed Ecuadorans’ lives, especially for the poorest citizens,” Moreno, a wheelchair user paralysed in a 1998 carjacking, triumphantly told supporters, before launching into an exuberant victory party at which he regaled the crowd with his singing.

Angry protests followed the first-round vote on February 19, when Moreno came close to winning outright and Lasso supporters cried fraud.

Correa presided over an economic boom that has recently gone bust.

“It’s a decisive moment because we’ve had a conservative reaction in recent years,” the outgoing president said after casting his ballot, adding that “the whole world is watching.”

In Latin America, where a so-called “pink tide” of leftist leaders has been ebbing, the vote is seen as crucial.

Argentina, Brazil and Peru have all shifted to the right in recent months, as the region has sunk into recession and leftist leaders have been tarnished by a string of corruption scandals.

Boosted by high prices for its oil exports, Ecuador registered solid economic growth averaging 4.4 per cent per year during the first eight years of Correa’s presidency, before tipping into recession in mid-2015.

Correa won loyal fans among the poor with generous social benefits that helped reduce the poverty rate from 36.7 per cent to 23.3 per cent in this country of 16 million people.

But he has also faced accusations of corruption and squandering the windfall of the oil boom.

Moreno, 64, won the first-round vote with 39 percent to Lasso’s 28 percent.

But Lasso, 61, united the opposition vote behind his promises to create a million jobs and eliminate 14 different taxes.

In another of the race’s hot issues, Lasso threatened to revoke the political asylum Ecuador has granted its most famous guest, Assange.

Correa, an outspoken critic of the United States, let the WikiLeaks founder stay at the London embassy to avoid arrest and extradition to Sweden over a rape allegation.

Assange waded into the electoral fray Sunday, congratulating Moreno and tweeting: “I cordially invite Lasso to leave Ecuador within 30 days (with or without his tax haven millions).”

That was a reference to WikiLeaks’s accusation that Lasso is linked to the Panama Papers tax haven scandal.

Assange, who denies the rape accusation against him, says he fears Sweden wants to send him to the United States to face trial for leaking hundreds of thousands of secret US military and diplomatic documents in 2010.