The top-seeded Novak Djokovic had a health scare in his third-round win over the 27th-seeded Taylor Fritz, injuring his abdomen as he slipped on the court midway through the third set. Visibly struggling, Djokovic needed five sets to prevail over Fritz.
Despite lingering concerns, and Djokovic saying that the injury would have forced him to pull out from the tournament were it not an all-important Grand Slam event, Djokovic has played well in his subsequent two matches, beating No. 14 Milos Raonic and No. 6 Alexander Zverev both in four sets.
His next opponent is a considerably less familiar one: Aslan Karatsev, a Russian who is playing in his first Grand Slam main draw at age 27, and has turned into the Cinderella story of the event.
Karatsev, who qualified for the Australian Open by winning three matches at a qualifying event in Qatar last month, has used clean, powerful groundstrokes off both wings to dismantle other players, including No. 8 Diego Schwartzman and No. 20 Felix Auger-Aliassime. Karatsev advanced to the semifinals after his quarterfinal opponent, No. 18 Grigor Dimitrov, was limited by back spasms.
Djokovic should be expected to advance comfortably if hes healthy, but if hes not, no player has proved quite as opportunistic as Karatsev.
Though decidedly an undercard to the preceding Osaka-Williams clash, the semifinal between Karolina Muchova and Jennifer Brady could also prove compelling.
Muchova, an all-court player, has been able to outlast many opponents playing near their top form, including the top-seeded Ashleigh Barty in the quarterfinals. After struggling with the heat and taking a medical timeout midway through the match, Muchova dominated the later stages, staying steady and purposeful on her powerful forehand as Bartys game went wayward.