Naomi Osaka breezed into the Gippsland Trophy semi-finals on Friday and saw the draw open up for her with defeats for Simona Halep and Elina Svitolina.

Osaka, the reigning US Open champion, was a 7-5 6-1 victor against Irina-Camelia Begu in the last eight to continue her winning start to the new season.

That run of successes stretches back 14 matches to last February, Osaka's only elimination in that time a walkover at the Western & Southern Open.

Unreliable weather also gave the second seed the opportunity to get to grips with playing under the roof at Margaret Court Arena.

"I feel like it’s more interesting that it’s different," the Japanese said.

"If I were to come out and for every day to be the same, I'm the type that gets bored, so a new challenge every day is definitely more interesting."

Elise Mertens is up next for Osaka after the Belgian defeated third seed Svitolina 6-3 5-7 10-6.

The other side of the draw is perhaps more intriguing still as Halep fell at the hand of Ekaterina Alexandrova while Karolina Muchova gave Kaia Kanepi a walkover.

Top seed Halep broke early and led 2-0 in the opener, only to lose 11 of the next 12 games in a stunning 6-2 6-1 defeat.

"I just tried to play my best," Alexandrova said. "I was kind of nervous at the start because this court isn't my lucky one, but after two games, I won one game and I felt much better."

At the Yarra Valley Classic, where Serena Williams' shoulder injury handed Ash Barty a place in the final, defending Australian Open champion Sofia Kenin saw her own preparations dealt a blow.

Kenin had the opportunity to lay down a marker when she faced Garbine Muguruza on Friday in a repeat of the 2020 Melbourne final.

But the American left the court in tears after a brutal 6-2 6-2 reverse that took Muguruza through to face Marketa Vondrousova for the right to take on world number one Barty.

"I knew it was going to be a very tough game from the baseline, because I remember very clearly the last match," Muguruza said.

"I was looking for it, I was more prepared for the biggest battle.

"I think I played better, I think I used my shots smarter and took my chances and I think I did well early, so I got the advantage of the score and then I kept playing well and dominating the match."