Novak Djokovic remained relatively untroubled as he moved on to the last 16 of the Miami Open with a 6-4 6-1 win over Joao Sousa.

The Portuguese player had been upgraded to 33rd seed after Martin Klizan's pre-tournament withdrawal, granting him a first-round bye which he followed up by beating Canada's Vasek Pospisil.

But he was no match for the world number one on the Stadium court and was dispatched in an hour and 18 minutes as Djokovic followed up his straight-sets win over Britain's Kyle Edmund.

The top seed broke serve five times, won 87 per cent of points on his own first serve and dominated the shorter rallies in particular to set up a clash with 14th seed Dominic Thiem, who ended the fine run of Japanese qualifier Yoshihito Noshioka with a 6-2 6-2 win.

Despite the one-sided scoreline against Sousa, Djokovic told atpworldtour.com: "He made me play. He made me push myself harder in the second set because he was staying close to the baseline and picking up the balls very efficiently, which I wasn't expecting.

"He was taking time away from me, especially from the side he was playing with the wind. He's a good player, he's very talented, he's very quick around the court; he served well."

The four leading seeds in the top quarter of the draw are all through as Richard Gasquet and Tomas Berdych, seeded 10th and seventh respectively, won their third-round matches.

Gasquet brushed aside fellow Frenchman Benoit Paire 6-3 6-0 in under an hour but Berdych was more sternly tested by Steve Johnson, eventually winning 6-3 6-7 (6/8) 6-3 in two hours and 43 minutes.

Horacio Zeballos continued to make the most of his privileged lucky-loser slot - having been inserted directly into the second round when third seed Roger Federer pulled out with a stomach virus, the Argentinian has beaten compatriot Juan Martin Del Potro and now Spain's Fernando Verdasco, 1-6 6-4 7-6 (7/4).

His next challenge will be David Goffin, after the 15th-seeded Belgian thumped Viktor Troicki 6-1 6-1.

Eighth seed David Ferrer was the day's highest-profile casualty, losing 6-7 (1/7) 7-6 (7/4) 7-5 by France's Lucas Pouille.

The world number 88 led by a break at 4-3 in the final set but was pegged back, only to eventually battle through after two-and-three-quarter hours on court.

He will play France's Gilles Simon, who beat Marin Cilic 6-3 6-7 (4/7) 6-3 in an equally lengthy tussle.

In the women's draw, Australian Open champion Angelique Kerber was sternly tested before illness ended opponent Kiki Bertens' challenge.

Bertens, ranked 41st in the world, beat 26th seed Anastasia Pavlyuchenkova in the previous round and took the first set 6-1 against the second seed - despite having been broken in the opening game.

But she needed a medical timeout early in the second set and though she battled on, Kerber gained the upper hand and was leading 1-6 6-2 3-0 before Bertens threw in the towel.

The German said in her on-court interview, reported on wtatennis.com: "Of course, it's always sad when the opponent retires; I hope she gets very well very soon, but I'm happy to be in the next round."

Timea Babos awaits her there after a 7-5 6-0 win over Japanese wild card Naomi Osaka.

Fourth seed Garbine Muguruza enjoyed a more comfortable evening on the Stadium court as she blew away American wild card Nicole Gibbs 6-1 6-0 to set up an enticing clash with 13th seed Victoria Azarenka.

The Belarusian was almost as dominant, beating qualifier Magda Linette 6-3 6-0.

British No.1 Johanna Konta battled past Elena Vesnina 4-6 6-1 7-6 (7/3) and will face Monica Niculescu, a 6-4 6-1 winner over CoCo Vandeweghe, however, Heather Watson crashed out after a straight-sets defeat to Simona Halep.

The British No.2 broke Halep in her first two service games and led 3-1 in the opening set before the world No.5 rattled off five straight games to take the first set 6-3.

Watson, currently ranked 69th in the world, was then broken again in the fifth game of the second set before breaking back to make it 3-3.

But yet another break put Halep 4-3 up before the pair held serve to give the Romanian the chance to serve for the match.

The 2014 French Open finalist then wrapped up the win with a love service game to advance into the quarter-finals.

Madison Keys eliminated ninth seed Roberta Vinci 6-4 6-4. The 22nd seed will take on Irina-Camelia Begu, who beat Kristyna Pliskova 7-5 4-6 6-4.