Australian Open champion Angelique Kerber bounced back after two early tournament exits when she won her second-round match at the Miami Open on Friday.

Business as usual was resumed as second seed Kerber dusted off Barbora Strycova 6-1 6-1 in barely an hos struggled since beating world No.1 Serena Williams in the Melbourne final to claim her maiden grand slam title in January.

She was part of the German Fed Cup team that lost to Switzerland, and in individual competition fell at the first hurdle in Doha last month and again last week in Indian Wells, an exit that gave her plenty of time to prepare for Miami.

“I worked very hard before Miami, because I had a lot of time after Indian Wells and I think the hard work pays off again,” Kerber said.

“At the end of such a great success it’s always good to celebrate a little bit and of course no one can ever take it away from me.

“But now it’s time to get on court and work hard again and do the same things that made me strong before Australia, getting ready for my next matches and tournaments.”

In other afternoon matches on Friday, fourth seed Garbine Muguruza of Spain was extended before outlasting Slovakian Dominica Cibulkova 6-7 (7-3) 6-3 7-5 in a marathon match that lasted nearly three hours.

Two seeds conceded defeat due to injury, with seventh seed Belinda Bencic of Switzerland and 18th-seeded Serbian Jelena Jankovic both retiring from their matches.

Sixth-seeded Spaniard Carla Suarez-Navarro also bowed out, losing 6-4 6-2 to American Coco Vandeweghe, as did 14th seed Sara Errani of Italy, who fell 6-1 6-3 to Japanese wildcard Naomi Osaka.

American tenth-seed Venus Williams also tumbled out of the tournament, losing to Russian qualifier Elena Vesnina 6-0 6-7 (7-5) 6-2.