Juan Martin del Potro extended his winning streak to 13 matches as he brushed aside Kei Nishikori to reach the last 16 of the Miami Open.

Del Potro, coming off his thrilling win in Indian Wells last week, needed just 72 minutes to triumph over his Japanese opponent 6-2 6-2.

With Roger Federer and Novak Djokovic having already exited the tournament, the fifth-seeded Argentinian is emerging as one of the favourites for the title.

And he lived up to that billing with another dominant display in which he faced just one break point and broke his opponent twice in each set.

Second seed Marin Cilic had to work harder for a 7-5 7-6 (7/4) win over Canada’s Vasek Pospisil which booked the Croatian’s place in the last 16.

South Korean Hyeon Chung is yet to drop a set in the tournament after requiring just 63 minutes to see off American qualifier Michael Mmoh 6-1 6-1.

The Next Gen Finals champion will next face Joao Sousa of Portugal, who beat another American, Jared Donaldson, 1-6 6-3 6-4.

Also in early action, 22nd seed Filip Krajinovic was a 6-3 6-3 winner over Benoit Paire of France.