Roger Federer's brilliant start to 2017 continued with an impressive win over Juan Martin del Potro in Miami.

The Australian Open and Indian Wells champion, who could make an unlikely tilt at regaining the world number one status later in the year, beat the Argentinian 6-4, 6-4 to advance to the fourth round.

Federer has lost just once this year after missing the last five months of last season with a knee injury and was always in control against Del Potro, whose forehand opportunities were restricted by the Swiss.

Federer is joined in the fourth round by his compatriot Stan Wawrinka after an easy outing for the top seed.

Wawrinka beat Tunisian Malek Jaziri 6-3, 6-3 and will meet rising star Alexander Zverev, who won an epic encounter against John Isner.

The German triumphed 6-7 (7/5), 7-6 (9/7), 7-6 (7/5), saving three match points, in a game that went on for two hours and 40 minutes.

Nick Kyrgios also prevailed in a titanic battle with big-serving Ivo Karlovic, winning 6-4, 6-7 (7/4), 7-6 (7/2).

Tomas Berdych beat Gilles Muller 6-3, 6-4, Roberto Bautista Agut came from behind to see off Sam Querrey 2-6, 6-2, 6-3 and David Goffin also fought back from a set down to beat Diego Schwartzman 3-6, 6-3, 7-5.

Frenchman Adrian Mannarino beat Borna Coric 6-4, 2-6, 7-6 (7/3).