It was the first triumph of 2008 for the fourth-seeded Canas, who was sidelined by a wrist injury. He will face another Argentine,
Jose Acasuso, who earlier defeated Spain's Oscar Hernandez, 6-4, 6-0.
"It's a pity I couldn't play the event last year, but now I am feeling good," said Horna.
Defending champion Juan Ignacio Chela, coming off a semifinal run in his Buenos Aires hometown last week, defeated qualifier Pablo Cuevas of Uruguay 7-6 (4), 6-4 and will face 2003 Acapulco champ
Agustin Calleri in the second round.
Austria's Peter Luczak defeated Argentina' Sergio Roitman 6-3, 6-4, Italy's Potito Starace defeated Ecuador's Nicolas Lapentti, 6-4, 6-2 and Italian Filippo Volandri bested Czech player Ivo Minar, 6-4, 7-5.
In women's play, all the favorites advanced.
Third-seeded Czech player Klara Zakopalova defeated Spain's Maria Jose Martinez, 4-6, 6-3, 6-1. Italy's fifth-seeded Sara Errani defeated Germany's Tatjana Malek, 6-3, 6-3, and Estonia's
Kania Kanepi (7), defeated Spain's Arantxa Parra 6-4, 6-3.
Romania's Edina Gallovits (8) defeated Mexico's Daniela Munoz 6-1, 6-0, and Czech Iveta Benezova defeated Sweden's Nadja Roma, 6-1, 6-1.