Nadal improved his record to 12-0 at this event, needing only 66 minutes to get past Lorenzi.
Nadal broke Lorenzi's serve five times and lost only five points on his serve, never facing a break point.
Nadal's opponent in the quarterfinals will be Yoshihito Nishioka of Japan, who eliminated Aussie Jordan Thompson 6-4, 3-6, 6-0. Nishioka defeated seventh-seeded Jack Sock in three sets in the first round.
Top-seeded Novak Djokovic faced a strong challenge from Argentina's Juan Martin del Potro on Wednesday, but the Serb emerged with a 4-6, 6-4, 6-4 victory.
