The Russian woman beat the American Madison Keys in three sets - 7: 6 (7: 4), 2: 6, 6: 3.
The meeting lasted 2 hours 13 minutes.
In the quarterfinals, Kasatkina will face the winner of the pair Nuri Parrizas-Diaz (Spain) - Claire Liu (USA).
Let's remind that the prize fund of the tournament in Melbourne is $ 239,477.
Earlier, Serbian President Aleksandar Vucic expressed support for the first racket of the world, Novak Djokovic, who was not allowed to enter Australia.