Serena Williams is two wins away from winning the Australian Open to tie Margaret Court for the most Grand Slam championships with 24. The first hurdle for the No. 10-seeded Williams is a semifinal matchup against No. 2 Naomi Osaka (10 p.m. ET, ESPN2).

Osaka already has prevented Williams from reaching the record 24th major championship once, when she pulled off a straight-sets upset in a controversial US Open final in 2018.

ESPN experts weigh in on the highly anticipated Williams-Osaka match.

Serena's fitness level and overall movement have been much improved this tournament. Where has that made the biggest difference in her game so far?

Mary Joe Fernandez: This is the best Serena has moved in the past few years. It has made the biggest difference in the fact that she doesn't have to go for shots that aren't there. She can hang in rallies better and wait for the right opportunity to be aggressive. She is more consistent as a result of her better defense.

Brad Gilbert: Serena's movement [in the quarterfinals] was the best I have seen her look since she has come back from having her daughter. Her defense and ability to defend was very big.

D'Arcy Maine: Serena has been able to run down every ball and contend in the long rallies. She joked she hasn't felt as good about her ability to do that since 1926 after her match against [Simona] Halep, and while it hasn't quite been that long, it's obvious how happy she is to be able to do that and the confidence it then gives her in all aspects of her game. Because of her improved mobility, some of the angles she was able to find against Simona Halep [in the quarterfinals] made me wish I had paid more attention in geometry class.

Jake Michaels: She's moving with much more freedom than we've seen in recent years and it's made her an even tougher proposition. Against Halep, we saw her track down balls from all over the court and pretty much beat the world No. 2 at her own game. It's hard to believe this Serena, probably the fittest she's been in Melbourne for at least five years, is 39.

Pam Shriver: Serena's overall fitness improvement is the biggest difference in her game, making it possible for her to have a better chance at tying Court's record 24 singles majors. As we saw during both the Aryna Sabalenka and Halep wins, Serena is playing much better defense, extending rallies and able to win with both her offensive and defensive skills. The past couple of years post-maternity leave, she was unable to play enough defense.

Rennae Stubbs: When you feel like you can grind one more ball back in the court and wait for the right one, you do. When Serena was at her best, that's what she did. She has the power to attempt a winner on almost every ball, but if you're not in the right position, it doesn't matter who you are, you will not be successful. So now with the extra speed and ability to hang in a little longer to wait for the right shot, it's making a world of difference. Also, an added feature to being slightly fitter is you mentally don't get as fatigued and, therefore, you make better decisions.

Matt Walsh: We all know how powerful Serena is and how damaging she can be when on the attack, but some of her defensive work this tournament has been unbelievable. She's been getting to balls that 39-year-olds should not be reaching, and it's made even more impressive given a throng of players have said this year's courts are the fastest they've ever seen in Melbourne.

How have both players improved since their last meeting at a Slam, the 2018 US Open final?

Fernandez: Naomi has improved all aspects of her game. Her serve is more powerful and her big weapon. Her backhand is more consistent and she can open court with the cross-court angles. Her movement is better as well. Serena's biggest improvement is her ability to defend better.

Gilbert: Osaka has dramatically improved her fitness and movement since that 2018 matchup.

Maine: Serena hasn't looked better since coming back from childbirth than she does right now. Her movement on court, her defense (I'm still not over this point from her match against Sabalenka), her ability to win the long rallies -- it's been very impressive. Perhaps most importantly, she seems to be brimming with confidence again and that could make a big difference. The 2018 US Open was Osaka's first major title and she's come so far since that time in adjusting to being the top dog. We saw her struggle after her win in Australia in 2019, but she's since found her rhythm and now knows what it takes to consistently win at this level.

Michaels: As mentioned, Williams looks to be fitter and moving much freer than we saw in that now-infamous final, which means it's only going to be a more daunting prospect for Osaka. But Osaka has gained a significant amount of experience, winning a further two majors since her maiden triumph at Flushing Meadows. The mental side of the game also looks to have improved significantly for Osaka in the past couple of seasons.

Shriver: Since Osaka and Serena played in the US Open final, Serena is better physically and emotionally. Even with the events that unfolded during that final, with the code of conduct changing the course of the match, Serena was not playing well enough to beat Osaka in that final. While Osaka played a wonderful first major singles final 30 months ago, she is a more skilled player today. Osaka has gained more patience, variety and fitness. Her serve is also more of a weapon now.

Stubbs: Serena is in a better place, I feel, emotionally and physically. I also believe she will be better prepared for the matchup tactically. Naomi, on the other hand, is so much more assured of herself emotionally; her confidence and maturity are through the roof compared to back in 2018. She is fully in control of her life, her legacies and her brand now, as well as her tennis.

Walsh: Osaka's composure has improved noticeably since that breakthrough, and it was plainly evident in her fourth-round match against an in-form Garbine Muguruza. Facing two match points down 4-5 in the third set, Osaka managed to recompose, and from that point went 22 points without an unforced error, eventually winning the match. For Williams, she seems to have embraced perspective really well as she gets into the twilight of her career, and looks to really be enjoying her tennis.

Fans are set to return to Melbourne Park for the women's semifinals. Will this be a help or hindrance for either player?

Fernandez: I actually think no fans helped Serena stay more focused and perhaps feel less pressure.

Gilbert: It will be interesting when fans return. It probably will benefit Serena but won't be a big deal for the outcome.

Maine: This match deserves a crowd, so from a fan perspective, we should all be thrilled for this development. However, neither player needs the extra motivation -- with a spot in the finals on the line, you can rest assured, they're all good there -- and for Williams, it actually might be somewhat distracting. She has talked about that throughout the tournament and mentioned how sometimes she gets anxious and nervous when the crowd is really into it during match point or other big moments. She will have to find a way to tune them out.

Michaels: I think it can only help the two. Let's be honest, both of them are used to playing in front of packed arenas, so it's not exactly going to be anything unfamiliar for either player. It's not as if fans will be leaving mid-match ala Novak Djokovic vs. Taylor Fritz!

Shriver: Fans returning to the AO will hurt Serena and help Osaka. Serena has said on ESPN this week that she feels an increase in anxiety with fans. Her play during the no-fan phase has been strong and focused. Osaka can more easily get into a zone needed to win, regardless if fans are in the arena or not.

Stubbs: I don't think it benefits any player. I honestly believe no crowd helps Serena stay calm, which to me is a must for her if she wants another Slam, as she has to control those emotions. Naomi is pretty shy and internally inside quite emotional, so no crowds also makes her calm. With the crowds, those emotions will return, so to me, it won't benefit either that much.

Walsh: I think given both players did play some (but not many) tournaments without crowds in 2020 but have also had limited crowds in Melbourne, it won't matter either way. Both players will be well supported in Melbourne regardless of crowd size.

You're coaching Serena heading into this match. What is your strategy?

Fernandez: Serena needs to get a high percentage of first serves -- over 60%, because she is winning about 80% of those points. That will allow her to take more chances on Naomi's serve. Once the point starts, it will be important for Serena to dictate with her forehand like she did against Simona Halep [in the quarterfinals].

Gilbert: It's crucial for Serena to serve strong and get free points. Once again defense will be key, as Osaka is probably the biggest hitter on tour.

Maine: I would just tell her to stay calm. Trust herself and her game and all the work she's done. Focus point by point and ignore the outside noise and the weight of the moment.

Michaels: Dictate the play. We saw Serena slap a return winner in the first point of the match against Halep and that sort of aggression needs to be on display against Osaka. Serena looked nearly unbeatable against Halep when she had the Romanian scrambling behind the baseline, and it's exactly what she needs to do against Osaka if she is to prevail and return to the Australian Open final.

Shriver: Serena needs to play all aspects of her game -- offense, defense and the mental game -- at her best level to beat Osaka. Serena will benefit from being on the half of the draw with a day off between quarters and semis. She needs to have a top-shelf serving day.

Stubbs: Go hard to the forehand, whether it's through the middle or getting Naomi running more to the forehand. Also, try and stay as calm and in control as you can throughout. Use the body serve slightly more than you usually do to back Naomi up and not allow her to attack your serve as much. Overall, take control and never let up.

Walsh: I'm not sure any advice I have for a 23-time Grand Slam winner is going to be good advice, but if there's one thing I will say, it's put the ball in positions where Osaka might make mistakes -- which is no easy task. That Osaka unforced error stat from the [Garbine] Muguruza match is outrageous -- Williams must keep her moving and give her no easy returns.

And for Osaka?

Fernandez: It's very similar for Naomi. First-strike tennis will be important. If she is serving well, that will put a lot of pressure on Serena. She will want to get into the crosscourt backhand pattern to open up the court.

Maine: No one really needs coaching advice from me, but I would emphasize to Osaka to not think about who is across the net. Don't think about this match as different from any other and play your game that has gotten you this far.

Michaels: It's important that Naomi start the match well. Sure, she is certainly capable of coming back from a set down, but Serena will only grow in confidence and ability as the match wears on. If Osaka is to win, she needs to plant the seed of doubt in Williams' mind early and not let the 23-time Grand Slam champion boss her around the court.

Shriver: Osaka needs to do what she has been doing in major tennis when she reaches the final stages: continue to play power tennis with the ability to hurt any opponent with both her ground strokes and her serve. She has not lost a semifinal of a major yet and I believe she is doing everything Serena does, but just a little bit better.

Stubbs: Believe in your ability to manage the power, take the ball through the middle of the court sometimes and force Serena back; make her play one more ball. Pressure the second serve when you can. Serve body on big points to mix it up.

Walsh: Play your game. She shouldn't need to do anything different to try and beat Serena -- there's a reason Osaka is favorite with the bookies and is expected to win this tournament despite not being the No. 1 seed.

Serena or Osaka: What is your prediction?

Fernandez: Osaka is the favorite but Serena keeps improving with each match. The better the opponent, the better she plays.

Gilbert: I picked Osaka to win the tournament two weeks ago and I'm staying with that, 6-4 7-6.

Maine: This is really tough. Serena is playing such amazing tennis, but Osaka feels almost unbeatable right now. Just ask Muguruza. Osaka in three sets, but I will likely change this answer several times before the match starts.

Michaels: I'll take Osaka in three epic sets. Williams has been playing some exceptional tennis at this tournament, but youth is on Osaka's side and she looks hungry for more Grand Slam success. Don't forget, every time Osaka has reached the fourth round at a major, she's gone on to win the title.

Shriver: Osaka is the winner.

Stubbs: Whoever serves a higher percentage will win. I believe Serena is playing and looking the best she has in years. This is going to be the biggest test for them both. I give a slight advantage to Serena, by a whisker.

Walsh: Osaka in a tight two sets: 7-6 (5), 7-5.