MELBOURNE, Australia -- We'd be lying if we said this match wasn't one of the first significant showdowns on our radar the moment the Australian Open draw was released. Turns out the results have played out as we had hoped, and now it's on: Serena Williams vs. Simona Halep.

Yes, the 23-time Grand Slam winner takes on the world No. 1 on Monday (3 a.m. ET on ESPN2) in a quarterfinal battle that's no doubt worthy of being the championship match Down Under.

So who has the advantage? That's a good question, which is why we asked a handful of experts around the grounds. Here's what they had to say:

What's the key for Halep?

Mary Joe Fernandez, former world No. 4 and current ESPN tennis analyst: She's going to have to serve well. Serena has been returning extremely well. A lot of first serves. When I saw them play in Miami a few years ago and it went the distance, that was one of the keys. I think she's going to have to hit a lot of body serves, not let Serena tee off, because Serena's seeing the ball really well. But Simona is going to have to extend the rallies. The key is if she can absorb that first shot, and then somehow take control of the point to move Serena. Serena's moving a lot better this year, but I still think that's where she can hurt Serena, especially moving to her right.

Chanda Rubin, former world No. 6: I think obviously her speed is her big strength and her ability to compete is a big part of her game as well. She's going to have to bring a certain level of intensity. I think she's going to have to try to stretch the court a little bit more, keep her moving, get her going and extend points as long as possible. And I think her serve will need to be firing, because that's something she uses to position herself in points. I think it will be dependent on how well she comes out with her level of intensity, how well she gets Serena moving.

Mark Hlawaty, former hitting partner of Serena Williams: I kind of get the feeling she has to be the brick wall and she's just going to force Serena to try to hit bigger and bigger, potentially closer to the lines. Halep is going to take on the role that I'm just going to hunt every ball down and it's going to be like a puppy with the little ball: wherever that ball goes, I'm going to go and try to retrieve and retrieve. Hopefully for Halep, that builds enough pressure where Serena will end up missing and then she'll be able to sink her teeth into it and maybe control a few more points. She's probably going to expect to lose some serves and may not get any real free points off it. But it's, "OK, I've got to get it in but then I've got to be ready to scramble and hustle and accumulate pressure that way." Serena's going to do the opposite, she's going to step on that baseline. Halep doesn't hit as big so she's probably going to have a swing at every opportunity, especially on second serve. It's a matter how aggressively controlled Serena can be.

Jelena Dokic, former world No. 4: I think the thing with Serena is the serve. That's the toughest thing you're facing; straightaway you're on the back foot. I've played Halep and I know what that's like, it's not just the power, but the accuracy and the consistency. She's going to have to expose the movement of Serena as much as she can, keep her out there, longer points, but I think it's going to be really hard.

Neither Serena nor Halep has played very much since the end of the US Open. How will that affect this match?

Serena Williams has dropped just nine games through three matches at this year's Australian Open. Fred Lee/Getty Images

Fernandez: For Simona, I think she does need matches. But I think the first few she had here were quite good, quite competitive, two three-setters, down a set and a break in the first one, and then she played really well against Venus. The fact that she played Venus will prepare her well for playing Serena. But she's the type of player who needs the reps; she needs to be out there kind of grinding and playing well. We've seen Serena win without playing much tennis, but she played those tough quality matches in the Hopman Cup, so that served her well. She just looks that much more consistent early in a major. Usually, you're not sure, she's vulnerable, but she's not looked vulnerable at all. It feels like a final. I can't believe it's the fourth round.

Rubin: I think with the way Halep's been playing -- she had some tough matches, the first two matches out of the gate, and then against Venus, it was the toughest draw you could have had. That's got to give her tremendous confidence and somewhat negates the need for having had additional matches. I think she's in a good rhythm, as good as she would expect coming in against Serena, with the three matches she came through, so I don't think it should be an issue.

Hlawaty: I think it probably affects Serena a little bit more. We don't know what her real fitness base is like. History says Halep is happy to be out there for five, six, seven days in a row to finish a match, and I think that's what she'll try to do, to keep her out there as long as possible, to test her out physically, and say, if you can do that for three hours, then good luck. Can she do that for three hours and sustain that kind of level?

Dokic: It's more normal for Serena. She's done it in her career, and she's gone into Grand Slams completely cold and won them in the past. She's done it after injuries. Simona, she hasn't really played in the last three months, took time off and had that back injury. That's a big problem. For her to only play one match in Sydney, she's talked about not being 100 percent here, that she's aware of that, she's not at her best, but I'm impressed how she's come through. To be in the fourth round, she's really sharp. Whether it's going to be enough, I'm not sure, but I think the matchup for Simona doesn't work so well and Serena has too many weapons.

What are you seeing in Serena that's different from last year?

Fernandez: She's much fitter, moving a lot better -- that's why she's not making as many mistakes. She doesn't have to rely on her serve so much because she's getting to balls and returning so well. She just looks that much more confident and back to what she looks like when she's the favorite.

Rubin: I think she's fitter. I think she's moving better. She just looks crisper, her first step -- and of course the customary intensity from Serena, we're seeing that every point and there's not too many letdowns. That being said, she hasn't really been tested, but those matches could have gotten a little tricky if she had let up a bit, so I really like the way she looks, the way she seems to be approaching her game. She's had matches, at the Hopman Cup and lead-up matches here, but she's just got to raise her level a little bit more.

Hlawaty: Yeah, she definitely looks fitter, stronger and she's had a relatively easy pathway through. I think that's good in a sense and she hasn't really been tested. This one is like, "My opponent has won a Slam, they know what to do, they can compete and she's got skills," but I think it's a better matchup for Serena than Simona.

Dokic: I've been really impressed with Serena here. She's gone into the tournament really sharp early on, which doesn't always happen with her. She's had a bit of a warm-up going from Hopman Cup and then some matches here, she's looking good. Having a Serena like this going into a second week is always dangerous. After her win yesterday, you'd have to put her as the favorite for the title. She's definitely moving a lot better than last year, but she played the Wimbledon final in only her fourth tournament back. It's only a little over a year since she gave birth. So we knew she was going to get better and better. But also I don't know, I see with her that her mental focus is really sharp. She always wants to win, but she looks like she's ready to win here.

Prediction?

Simona Halep played the best tennis of this year's Australian Open in her last match against Venus Williams. TPN/Getty Images

Fernandez: I think it's going to be close, but I think Serena's going to win.

Rubin: It's a tough one. I probably would lean toward Serena, just because of the weapons, the way she's playing, the way she's moving, but it'll be interesting. I think Halep's certainly going to make things difficult, and if she comes through that one, she's got to be certainly the favorite at that point.

Hlawaty: Watching Serena the other day you'd have to go with her, with that pace and aggressiveness. I think she wins in three sets.

Dokic: You'd have to put Serena as the favorite. I know Simona's No. 1 in the world. If she had not had that break, I'd say the match would be a lot closer, so I have to go with Serena.