Australian Open 2017: Champion Angelique Kerber cruises into last 16

Kerber beat Pliskova's twin sister Karolina in last year's US Open final

Defending champion Angelique Kerber gave a much-improved performance as she beat Czech Kristyna Pliskova for the loss of just four games to reach the last 16 at the Australian Open.

The German top seed, who needed three sets in both of her opening two matches, won 6-0 6-4 in Melbourne.

Kerber faces Coco Vandeweghe in round four after the American beat Canada's Eugenie Bouchard 6-4 3-6 7-5.

Venus Williams, 36, and Garbine Muguruza, 23, also progressed.

Williams thrashed China's Duan Yingying 6-0 6-1 while French Open champion Muguruza, the seventh seed from Spain, won 6-2 6-4 against Anastasija Sevastova.

Russian eighth seed Svetlana Kuznetsova was another winner early on day five, needing three hours and 36 minutes to beat Serbia's Jelena Jankovic 6-4 5-7 9-7.

"Jelena was in total control in the third set but I was trying to hang in, it was amazing that I could turn it around," said Kuznetsova, who trailed 3-0 in the final set.

"I just waited and tried to recover some breaks. I was not playing my best."

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Rhythm returns for world number one

Kerber finally got into her stride with a crushing win over Kristyna Pliskova, the 58th-ranked twin sister of Czech fifth seed Karolina.

After early defeats in both of her warm-up tournaments, and three-set battles in the first two rounds in Melbourne, the world number one appears to have found her game.

"It's great to have another good match under my belt and to be in the fourth round again here," said the German.

"I'm looking forward to the next one. I think that I'm finding my rhythm in the tournament now. I think it was a little bit up and down, the first week."