Australian Open champion Kerber advances in Miami heat

Second seed Angelique Kerber advanced to the fourth round of the Miami Open when Dutch qualifier Kiki Bertens was forced to retire in the third set on Sunday.

Bertens dominated the World No 3 in the opening set, but the 24-year-old became unwell early in the second set and was forced to take a medical timeout.

She eventually retired with an illness in the final set to hand Kerber a 1-6, 6-2, 3-0 win on another steamy day in south Florida.

"I think Kiki's a great player," Australian Open champion Kerber said in her on-court interview.

"She played very well in the first set and I was not finding my rhythm at the beginning.

"For me, it's not so easy. But I'm trying to focus on my game, doing my stuff and not looking too much over the net.”

Up next for the German is unseeded Hungarian Timea Babos, who advanced with a 7-5, 6-0 win over Japanese wildcard Naomi Osaka.

Other third-round winners on Sunday included American Madison Keys, Victoria Azarenka of Belarus, and Briton Johanna Konta.

Keys, the 22nd seed, upset ninth seeded 2015 US Open finalist Roberta Vinci of Italy 6-4, 6-4.