Then there's the two grand slam titles that separate the pair.

While 30th seed Pavlyuchenkova is thrilled to be back in the last eight at Melbourne Park for the third time, Muguruza has much bigger intentions despite being unseeded at a major for the first time since the 2014 French Open.

"It's one of the grand slams that one day I would like to win. It's exciting," the Spaniard said.

Winner of the 2016 French Open and 2017 Wimbledon crown, the former world No.1 is something of a forgotten star in women's tennis.

Even she had serious doubts about her ability to contend this year after arriving in Melbourne feeling ill and less than ready.

But after dropping her opening set of the tournament 6-0 to American Shelby Rogers, then losing another set to Australian Ajla Tomljanovic in the second round, Muguruza has looked unstoppable.

The world No.32 barely raised a sweat in taking out ninth seed Kiki Bertens last round after also dumping fifth seed Elina Svitolina from the draw in straight sets.

"I feel good in this tournament. I'm super concentrated on every single match, especially because I started the tournament so-so," Muguruza said.

"I feel like my body's getting healthier.

"It's a grand slam, we are all very concentrated here. For me, it's one of the tournaments that motivates me the most."

Two years Muguruza's senior at 28 and two spots higher in the rankings, Pavlyuchenkova has been super impressive herself.

The Russian removed second seed Karolina Pliskova in the third round, then backed up to belt 71 winners to dismiss 2016 Open champion and former world No.1 Angelique Kerber to repeat her run to the quarter-finals last year and in 2017.

But without a win in five meetings with Muguruza and also sans her opponent's grand slam silverware, Pavlyuchenkova isn't getting ahead of herself.

"Let me be humble here. I'm not going to say, I'm not playing my best tennis, not at all," she said.

"I feel like I play good tennis. But I still feel like I can improve a lot of things.

"I put it this way. Disciplined. Just fighting. Doing your job pretty much, doing what you have to do."

Muguruza or Pavlyuchenkova will play the winner of Wednesday's other quarter-final between Romanian fourth seed Simona Halep and Estonia's Anett Kontaveit.

Australian Associated Press