Kvitova needed less than an hour to get past American teenager Amanda Anisimova 6-2 6-1 on Sunday and hasn't dropped a set this tournament.

The world No.6 will meet Barty on Tuesday for the second time in a little over a week after beating the 22-year-old to win the Sydney title.

Kvitova, into the last 16 at the Australian Open for the first time since 2012, barely raised a sweat against the 17-year-old Anisimova.

"I think I work pretty hard on it," the two-time Wimbledon champion said of her fitness.

"It's a long life process to be still fitter and fitter. I'm feeling great. I'm not injured at all, which is the best I can have. I feel great."

Barty staged a rousing comeback to get past Maria Sharapova 4-6 6-1 6-4 in almost two and a half hours, but it was a much easier fourth-round outing for Kvitova.

World No.87 Anisimova, the youngest player to make the final 16 at the Australian Open in 13 years, had beaten 11th seed Aryna Sabalenka on an eye-catching run and loomed as a tricky opponent to the Czech.

But Kvitova broke in the opening game and didn't let up.

It was payback of sorts after Anisimova stunned Kvitova in the second round of Indian Wells last year.

"It is always pressure out there when you are favourite for the match," Kvitova said after extending her 2019 winning steak to nine matches.

"You never know how the young players are playing and they are here, nothing to lose. They are playing really fearless.

"That's how I remember myself when I was younger."

Kvitova, who fell out of the top 20 in 2017 after suffering tendon and nerve injuries in her hand in a knife attack, is within sight of her career-high No.2 ranking.

"I'm serving pretty well and I'm moving well. I'm really enjoying it to be on the court," she said.

Australian Associated Press