Miami Open: Roger Federer beats Juan Martin del Potro, Garbine Muguruza retires

Federer is playing in Miami for the first time since 2014

Roger Federer took his 2017 record to 15 wins from 16 matches as he beat Juan Martin del Potro at the Miami Open.

The Swiss, 35, won 6-3 6-4 to reach the last 16, where he will face Spanish 14th seed Roberto Bautista Agut.

"I feel like I earned it more," said Federer, the champion in 2005 and 2006. "I was more the aggressor. It was more my racket, and I like it that way."

In the women's singles, German top seed Angelique Kerber beat Risa Ozaki of Japan 6-2 6-2.

• Briton Konta into Miami quarter-finals

'I started to feel dizzy'

Muguruza was tended to by doctors after a 70-minute opening set

Twelfth seed Caroline Wozniacki of Denmark progressed after Spanish sixth seed Garbine Muguruza retired when feeling dizzy in the heat at 7-6 (7-1) down.

"I started normal, and then like at 3-3 or something like this I started to feel headache, pain in my stomach," said Muguruza. "And then it kind of went more and more during the match.

"When I was getting to the 5-4, something like this, I started to feel a little bit dizzy. I think it was the heat. The heat affected me suddenly like that."

Wozniacki will next face Czech Lucie Safarova, who beat Slovakian fourth seed Dominika Cibulkova 7-6 (7-5) 6-1, while Czech second seed Karolina Pliskova brushed aside compatriot Barbora Strycova 6-1 6-4.

Venus Williams, who last won the tournament in 2001, saw off Svetlana Kuznetsova 6-3 7-6 (7-4).

In the men's singles, top seed Stan Wawrinka, who has never won the event, overcame Tunisia's Malek Jaziri 6-3 6-4, while Australian Nick Kyrgios edged past Ivo Karlovic in a deciding tie break 6-4 6-7 (4-7) 7-6 (7-2).

Czech 10th seed Tomas Berdych beat Luxembourg's Gilles Muller 6-3 6-4 and goes on to play Frenchman Adrian Mannarino.