The Spaniard made short work of Dodig, eventually winning 6-3 6-3 to claim his 41st straight win in Barcelona – a record which stretches 11 years.
The world number one earned the first break of the match in the fifth game to edge into a 3-2 lead, before fighting back from 15-40 to take the first set.
Nadal then raced into a 4-1 lead in the second, and eventually wrapped up the win in 83 minutes.
He told reporters after the tie: "I still have work to do but the intensity on the legs was better. I was more relaxed."
Nadal will now meet Nicolas Almagro in the quarter-finals.