Cardoso covered the 159.2 kilometers of the route in 4:34.5s as he swept to a hugely impressive stage victory in the race.
Enrique Sanz of Spain and Francisco Jose Pacheco finished in second and third after a bunched group of riders sprinted to the finish.
Leon Deyser Gyos Kastro was another spot back, but it was Cardoso who took the spoils on the opening day.
1. Manuel Cardoso (POR) Caja Rural 3:44:55
2. Enrique Sanz (ESP) Movistar +4
3. Francisco Pacheco (ESP) Gios +6
4. Danilo Napolitano (ITA) Acqua & Sapone +10
5. Sergio Ribeiro (POR) Efapel +10