International election observer Martin Sequeira said voting proceeded calmly with a high turnout.
He said there were some unconfirmed reports of election fraud complaining that some ballots had been pre-marked.
However, Arias said those were only “some small incidents, which you see even in the most consolidated democracies.’”
Cartes, who takes office on Aug. 15, is a newcomer to politics. He did not join the Colorado party until 2009, and says he voted for the first time in 2008.
Additional reporting by AP