The Spanish veteran fired past Russian 30th seed Anastasia Pavlyuchenkova 7-5 6-3 while a ruthless Halep crushed Estonia's Anett Kontaveit 6-1 6-1 in Wednesday's earlier quarter-final at Rod Laver Arena.

Currently ranked world No.32, both Muguruza and Halep are former Wimbledon and French Open champions.

Halep has come closest to a title at Melbourne Park, losing the 2018 decider to Caroline Wozniacki in a three-set heart-breaker.

She fired a warning that she won't let another opportunity slip, needing just 53 minutes to oust Kontaveit in a flawless display.

Kontaveit didn't play that badly - only making 15 unforced errors - but Halep hunted down every ball and sent it back with interest.

The Romanian said she was feeling stronger than ever.

"I played my best game on court, I felt strong in my game, strong in my legs," said the world No.3.

"I worked a little bit more in the off-season - for the first time in my life I did the off-season away from home so I could be focused on what I have to do every day, no days off.

"That meant a lot for me and this year, I started very well and I am feeling much stronger than before."

Muguruza, whose last major semi-final appearance was at Roland Garros in 2018, had a tougher time against Pavlyuchenkova.

The pair traded breaks early in the second set before 26-year-old Muguraza stepped up her play.

A double-fault by the Russian handed her opponent a 2-4 lead and she was never headed from there.

"Definitely I had adapt to the circumstances. Sometimes you don't feel great but you got to fight and stay there and the first set was very hard," Muguruza said.

"I think it lasted like an hour. So it was a very important set and I'm happy I got it.

"I'm happy to play tomorrow. Don't wait another day and excited to play here in my first semi-finals."

Australian Associated Press