Jannik Sinner of Italy celebrates after defeating Holger Rune of Denmark in their fourth round match at the Australian Open tennis championship in Melbourne, Australia.

Holger Rune of Denmark plays a forehand return to Jannik Sinner of Italy during their fourth round match at the Australian Open tennis championship in Melbourne, Australia.

Jannik Sinner of Italy plays a forehand return to Holger Rune of Denmark during their fourth round match at the Australian Open tennis championship in Melbourne, Australia.

Holger Rune of Denmark plays a forehand return to Jannik Sinner of Italy during their fourth round match at the Australian Open tennis championship in Melbourne, Australia.

Elena Rybakina of Kazakhstan serves to Madison Keys of the U.S. during their fourth round match at the Australian Open tennis championship in Melbourne, Australia.

Madison Keys of the U.S. plays a forehand return to Elena Rybakina of Kazakhstan during their fourth round match at the Australian Open tennis championship in Melbourne, Australia.

Elena Rybakina of Kazakhstan plays a forehand return to Madison Keys of the U.S. during their fourth round match at the Australian Open tennis championship in Melbourne, Australia.

Madison Keys of the U.S. plays a backhand return to Elena Rybakina of Kazakhstan during their fourth round match at the Australian Open tennis championship in Melbourne, Australia.

Elina Svitolina of Ukraine plays a forehand return to Veronika Kudermetova of Russia during their fourth round match at the Australian Open tennis championship in Melbourne, Australia.

Ben Shelton, right, of the U.S. shakes hands with Gael Monfils of France after Monfils retired during their fourth round match at the Australian Open tennis championship in Melbourne, Australia.

Gael Monfils of France plays a forehand return to Ben Shelton of the U.S. during their fourth round match at the Australian Open tennis championship in Melbourne, Australia.

Ben Shelton of the U.S. reacts after winning a point against Gael Monfils of France during their fourth round match at the Australian Open tennis championship in Melbourne, Australia.

Iga Swiatek of Poland waves after defeating Eva Lys of Germany in their fourth round match at the Australian Open tennis championship in Melbourne, Australia.

Iga Swiatek, right, of Poland talks with Eva Lys of Germany following their fourth round match at the Australian Open tennis championship in Melbourne, Australia.

Alex de Minaur of Australia plays a forehand return to Alex Michelsen of the U.S. during their fourth round match at the Australian Open tennis championship in Melbourne, Australia.

Alex Michelsen of the U.S. reacts during his fourth round match against Alex de Minaur of Australia at the Australian Open tennis championship in Melbourne, Australia.