The second-seeded Nadal needed just 85 minutes to beat Alund at the clay court tournament and will next face another Argentine in Leonardo Mayer, who defeated Russia's Andrey Kuznetsov 6-2, 6-2 to advance.
Top-seeded David Ferrer beat American Wayne Odesnik 6-2, 6-1 to reach the final eight.
Nadal is making a comeback after being away from the tour for more than seven months with a left-knee injury. He made the final of the VTR Open earlier this month in Chile before losing to Argentine Horacio Zeballos. A week later he beat David Nalbandian to claim the Brazil Open title.