Pliskova, Sabalenka into Open's last 16

Former world No.1 Karolina Pliskova feels like she is slowly warming to the task after storming into the Australian Open's second week for the first time in four years.

Runner-up to Ash Barty in the 2021 Wimbledon final, Pliskova pounded down six aces and bossed Varvara Gracheva from the back in a 6-4 6-2 dispatch of the Russian on Saturday.

The Czech landed 72 per cent of her first serves and won 82 per cent of those points in an ominous warning to her rivals.

"My serve, it can be a really good weapon ... and I'm not doing as much running from the baseline," 30-year-old Pliskova said.

The WTA's perennial annual ace-leader will play Zhang Shuai on Monday for a place in the quarter-finals after China's 23rd seed ended the run of American qualifier Katie Volynets 6-3 6-2.

Belinda Bencic, who opened the season with success at the Adelaide International 2, also advanced after extending her winning streak to eight matches with a 6-2 7-5 victory over Camila Giorgi.

"Just happy to be in the second week," Bencic said.

The Swiss world No.10 faces Adelaide International 1 champion Aryna Sabalenka next in a test of both in-form stars' Open title credentials.

Fifth-seeded Sabalenka outclassed Belgian Elise Mertens 6-2 6-3 to rack up her seventh successive straight-sets victory of the year.

"That's a great stat but I'm just focused on myself, trying to keep it up," the Belarusian said.

"I'm super happy to be here showing my good level in front of you guys.

"I'm playing a little bit better than last year and that's probably why I'm enjoying it more."

French fourth seed Carolina Garcia recovered from a poor start to beat Laura Siegemund 1-6 6-3 6-3 to reach the second week for only the second time in 12 visits to the Open.

Garcia will meet Polish world No.45 Magda Linette, who upset 19th seed Ekaterina Alexandrova 6-3 6-4 to advance to the fourth round of a grand slam for the first time.

Donna Vekic also progressed, matching her effort from 2021, with a 6-2 6-2 disposal of Spaniard Nuria Parrizas Diaz.

Vekic has reached the last 16 of all four slams and, finally injury-free again, has a golden opportunity to secure a maiden quarter-final berth in Melbourne.

"I am really happy with my match today. I love this court," the Croatian said.

"The last time I was here two years ago I had a lot of pain in my knee so I am happy to be walking out on this court playing free today."

The 26-year-old world No.64 lost to eventual runner-up Jennifer Brady two years ago.

On Monday, Vekic will play unseeded Linda Fruhvirtova after the teenage sensation took out Czech compatriot and French Open finalist Marketa Vondrousova 7-5 2-6 6-3.