The election result follows the most recent comeback earlier this month in Nicaragua of the Cold war enemy of the US, Daniel Ortega.
Left-leaning leaders, some more moderate than others, govern in Argentina, Bolivia, Brazil, Chile, Cuba, Uruguay, as well as Nicaragua and Venezuela, where Chavez looks certain to win re-election on Sunday after eight years in office.
Correa, a US-trained economist, had earlier announced victory and told a news conference in Quito: "Thank God, we have triumphed. We are just instruments of the power of the people. This is a clear message that the people want change."
"We are just instruments of the power of the people. This is a clear message that the people want change"
Feature: Left foot forward
He said he would keep his promise to carry out widespread reforms which include re-negotiating debt agreements, opposing a US free-trade pact and re-writing the constitution.
He later told reporters in his tropical home city Guayaquil: "The people have given us a clear mandate, with the second-largest margin in the last 30 years of democracy.
"We want a deep political reform."
Correa won a place in Sunday's run-off by pledging a "citizens' revolution" against the discredited country's political system.
Ecuadoreans have driven the last three elected presidents from power, and Correa appealed to voters as a fresh face in a field of established politicians.
He has pledged to construct 100,000 low-cost homes and copied Noboa's promise to double to $36 a "poverty bonus" that 1.2 million poor Ecuadoreans receive each month.