Daria Kasatkina and Natalia Zabiiako's YouTube vlog has been a runaway hit with fans and players alike -- and it's even the reason behind Kasatkina's friendship with Jelena Ostapenko.

Kasatkina also beat Ostapenko in the third round of last year’s U.S. Open and defeated Garbiñe Muguruza, the 2017 Wimbledon champion, on her way to the final in Dubai last month.