World number one Simona Halep insisted she will have nothing to lose when she takes on Serena Williams in the fourth round of the Australian Open.

After battling through two tough opening rounds against Kaia Kanepi and Sofia Kenin, Halep knew she would have to step things up against Venus Williams and she did so impressively in a 6-2 6-3 victory.

In what must surely be the toughest draw a top seed has ever faced, Halep now finds herself taking on Serena, who has lost only nine games in three matches and demolished 18-year-old Dayana Yastremska 6-2 6-1.

Halep may have the number one next to her name but she has won only one of her nine previous meetings with Serena and feels she goes in as the underdog.

The Romanian said: "In my opinion, to be number one in the world and to be the best player in the world, it's a little bit different. In this moment, I'm number one in the world, so I will take that.

"But, for sure, she's the best player in the world because she won so many grand slams. She's been a lot at number one. I cannot compare my results to her.

"Definitely it's the toughest draw I've ever had. Every time I face the sisters is a big challenge for me. I just want to try to play my best tennis because I have nothing to lose against them.

"It's going to be just a huge match for me. I will not put pressure on myself. There's a good chance for me to play my best tennis and to feel good on court."

Serena and Halep have not met since before the former's break from the sport to give birth to her daughter, and she, too, is looking forward to testing herself.

"It will be great," said Serena. "I haven't played the world number one since I've been back. So it will be good."

While the title favourite continued to steamroller her way through the draw, Naomi Osaka and Elina Svitolina both survived serious scares to reach the last 16.

Osaka was a set and 4-1 down to the tricky Hsieh Su-wei before winning 11 of the last 12 games in a 5-7 6-4 6-1 victory.
Svitolina, who was again watched by boyfriend Gael Monfils, was arguably even closer to the exit door and struggling with a shoulder issue against Zhang Shuai.

The sixth seed trailed 3-0 in the third set before coming back to lead 5-3, failing to serve out the match and then eventually winning 4-6 6-4 7-5 in almost three hours.

Asked what her mindset had been in her on-court interview, Svitolina said: "I'm going to die or win."

She added later: "I think, 'OK, there is an opponent across the net, and also struggling in the same situation, also running the same amount of hours on the court'. So I try to think that way and I'm not alone here in hell."

Zhang had plenty of opportunities to really put the hammer down but could not quite do it and Svitolina went over to her Chinese opponent after the match to offer some consoling words.

"She's a very nice person," said Svitolina, who next faces 17th seed Madison Keys after her victory over last year's semi-finalist Elise Mertens.

"It's not only about tennis here. I think it's very important to be a person and to be open. When someone is hurting, it's normal to help."

Osaka next faces 13th seed Anastasija Sevastova, who she beat in three sets at the warm-up tournament in Brisbane.

The US Open champion was proud of her response in adversity against Hsieh, saying: "Of course I'm happy with how I fought.

"For me, that's one of the biggest things I always thought I could improve, because it sort of seems like before I would accept defeat in a way."

Garbine Muguruza backed up her late-night win over Johanna Konta by seeing off Timea Bacsinszky 7-6 (5) 6-2.