Nadal, in comeback mode after missing seven months with a knee injury, moving on to the quarterfinals when he breezed past Brazilian qualifier Joao Souza 6-3, 6-4. He will face Carlos Berlocq of Argentina, who beat eighth-seeded Albert Ramos of Spain 7-6 (9-7), 6-4.
Nadal made the final of his first post-layoff tournament last week at Vina del Mar, Chile, but was upended there by Argentina's Horacio Zeballos.
Second-seeded and world No. 11 Almagro unleashed 18 aces in getting past Chilean qualifier Paul Capdeville 6-4, 6-7 (3-7), 6-2 on Day 4 in Sao Paulo. He advances to take on former Wimbledon runner-up David Nalbandian, who breezed by fellow Argentine Guido Pella, 6-4, 6-2.