Iga Swiatek took just 49 minutes to beat "best friend" Kaja Juvan and reach the US Open fourth round.
The pair have known each other since they were teenagers but defending champion Swiatek was ruthless in a 6-0 6-1 victory in New York.
Top-ranked Swiatek made only one unforced error in the first set and dropped just 15 points in the match.
"It is literally like playing against your sister because we've known each other for so long," the Pole said.
"I didn't like the fact that I was winning against my best friend, but I knew that I have to be really focused and not let myself think about that.