Contrasting stakes in Aussie Open women's semifinals

— -- The women's semifinals at the Australian Open are a study in contrasts, one match featuring the two highest seeds in the upper half and the other a pair of newcomers to the final four Down Under. In the case of Johanna Konta, she's a newbie to a Grand Slam semifinal, period.

Here is a look at how the matches shape up:

No. 1 Serena Williams versus No. 4 Agnieszka Radwanska

ESPN2/WatchESPN: Watch Serena-Radwanska match live, 9:30 p.m. ET

The last time these two players met at a Grand Slam event, Serena Williams ended up claiming her 14th Grand Slam title, in 2012 at Wimbledon. The positives for Radwanska? She was in a major final, and she forced a match against Serena to three sets for the first time.

But Radwanska hasn't been back to a Grand Slam final since, nor has she won another set against Williams. While the inventive 26-year-old has been the most successful WTA pro since the 2015 US Open, it's difficult to see how she might navigate her way to that breakthrough first win against Williams after eight losses.

Williams is on fire now, and she has always had too much of everything that matters for the crafty Radwanska to subvert her anyway. You can expect Williams to tee off on Radwanska's serve, driving her back and off the court. The theme once again is that Radwanska can run, but she can't hide. It somehow seems fitting that Radwanska leads the tournament in break points converted, but she'll be facing the woman most capable of wiping away those dangerous points before her opponent can work a point.

Nevertheless, we saw the kind of trouble Williams could get into at the majors last year. And Radwanska, who is on the short list for "best player who hasn't won a major," is playing some of the best tennis of her life. She has won 27 of her past 31 matches, including the WTA Finals in Singapore. Earlier in this tournament, Radwanska recovered to win from a perilous 2-5 deficit in the third set.

Those are details that could make any player feel like Superwoman. Unfortunately, there's already a Superwoman on the WTA tour and her name is Serena Williams.

No. 7 Angelique Kerber versus No. 47 Johanna Konta

ESPN2/WatchESPN: Watch Kerber-Konta match live (after first match)

This will be the first meeting between two players who are bound to feel some degree of anxiety -- Konta because she's never been this far at a major (she lost in the first round in six of her previous eight main-draw appearances), and Kerber because she'll be expected to roll through the match to reach her first Grand Slam final.

The bigger the opportunity, the bigger the pressure.

Kerber made just 16 unforced errors in her quarterfinal win against Victoria Azarenka, and once again had to fight off the mental yips in each set. Kerber will have to prove she can keep her composure against Konta, a player who has enough power to be dangerous against anyone.

Kerber was especially strong defending her second serve against the aggressive returns of Azarenka, winning 56 percent of her second-serve points compared to 38 percent by Azarenka. Kerber would benefit from being equally efficient against Konta, who likes to attack the serve, as she showed in her quarterfinal win against Zhang Shuai, who won just 44 percent of her first-serve points and fared even worse on the second serves.

Kerber has been trying to play more aggressively and has worked hard to improve her serve. If she can put Konta under pressure early, the underdog might get rattled, but attacking comes naturally to Konta, owing partly to her big serve. She likes to bring the heat up at around 110 mph, so Kerber will need to be dialed in on her return, especially on first serves.

A lot will depend on how Konta handles what is by far the biggest moment of her rapidly blossoming career. She burst onto the scene late last summer and appears to be here to stay, although at 24 she's certainly no prodigy.

Kerber would sympathize, having made her own major breakthrough at the same age in 2012. But that will be the furthest thing from her mind Thursday.