Two-time defending champion Novak Djokovic moved into the last 16 of the Miami Open after a comfortable straight-sets victory against Joao Sousa on Sunday. 

The world number one needed just one hour, 18 minutes to get past his Portuguese opponent 6-4 6-1 at the ATP 1000 event.

Sousa made a promising start, holding serve three times, but was broken in the fourth game by Djokovic. 

Djokovic - who fired down nine aces - was looking lethal on serve but Sousa managed to break in the next game, however the Serbian went on to claim the first set by reeling off consecutive games.

The second set was far more routine for Djokovic, with the five-time champion sealing it six games to one, winning an impressive 92 per cent of points from his first serve.

The 11-time grand-slam champion will face Dominic Thiem in the next round after the Austrian 14th seed eased past Yoshihito Nishioka 6-2 6-2.