MELBOURNE, Australia - World No.1 Simona Halep will face 23-time Slam champion Serena Williams in the Round of 16 at the Australian Open on Monday. It's a blockbuster showdown between the two marquee stars, booked after Halep defeated Venus Williams 6-2, 6-3 in the third round on Saturday night. And it means that Serena's historic quest for Slam No.24 will have to go through the World No.1.

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

Halep did precisely that in her solid win over Venus, her third in a row over the American. 

"I think she played pretty flawless today," Venus said. "Only 12 errors. Unfortunately, I had almost three times as many. Just needed to keep my errors down. But she played a great match."

This will be Serena's first match against a World No.1 since her return last March from maternity leave. In fact, she has not faced a World No.1 since 2013, a loss to then No.1 Victoria Azarenka in the final of Doha. Serena is 6-1 in her last seven matches against reigning No.1s, dating back to 2008.

"I honestly would love to face the World No. 1," Serena said. "It will be great. I haven't played the world No. 1 since I've been back, I don't think. So it will be good."

"In this moment, I'm No.1 in the world, so I will take that. I feel like I have been there many months, many weeks. But for sure she's the best player in the world because she won so many Grand Slams."

- Simona Halep

Halep goes into her fourth-round showdown against Serena as the World No.1, but she says she'll be standing across the net from the best player in the world.

"In my opinion, to be No. 1 in the world and to be the best player in the world, it's a little bit different," Halep explained. "In this moment, I'm No.1 in the world, so I will take that. I feel like I have been there many months, many weeks.

"But for sure she's the best player in the world because she won so many Grand Slams. She's been a lot at No.1. I cannot compare my results to her. 

"But in this moment, I am confident that I am in this position, and I'm positive about it."

Halep will become the 13th player to face both Serena and Venus at a major and just the 9th to do so in consecutive rounds. Only four players have ever defeated Serena and Venus in a major - Kim Clijsters, Justine Henin, Martina Hingis, and Karolina Pliskova - and only two players have defeated the sisters in back-to-back matches at a major: Justine Henin (2007 US Open) and Martina Hingis (2001 Australian Open).

Serena has won eight of her nine meetings with Halep, a head-to-head record that Halep could only laugh about. 

"We had also tough matches together," Halep said. "So 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.

Halep's lone win over the American came at in the group stages of the 2014 WTA Finals, a 6-3, 6-0 win. But the two have not faced each other since 2016. Their last match came in the quarterfinals of the US Open, a compelling battle that saw Serena prevail 6-2, 4-6, 6-3.

"It's going to be huge challenge for me," Halep said. "It's always great to play against Serena because every time I have to learn something from the match.

"I think I have to play similar [as she did against Venus], if I can. I have to be smart, aggressive. I have to move her and give my best. I will not super think about this because is nothing to think, just go there and play natural and with confidence."

Asked whether Serena's limited tournament play since her return from maternity leave last March might prove her vulnerable on Monday, Halep refused to take the bait. 

"For sure is not easy if you play less tournaments," Halep said. "But she has enough experience to handle every moment of the matches. So I don't believe she's vulnerable because of that.

"I didn't play against her since she came back, so I don't know what to say about this. She's a very tough opponent every time."

"I'm used to this pressure. I'm used to face her. I'm in a good position. I feel confident. 

"I played very well today. But doesn't mean is going to be the same against her.

"I will wait. I will focus on myself. It's the most important thing. I will see what is going to happen on court."