World number one Iga Swiatek demolished "best friend" Kaja Juvan in straight sets on Friday to march into the last 16 at the US Open.

Swiatek, who has been a close friend of Juvan since her youth tennis playing days, showed no mercy to the Slovenian world No.145 with a 6-0, 6-1 victory on the Louis Armstrong Stadium.

"For sure I didn't like the fact I was winning with my best friend," Swiatek said afterwards. "It was like playing against a sister because I've known her for so long. 

"I don't have many friends but she's my best friend."

The 49-minute drubbing sends defending champion Swiatek into a fourth-round meeting with either Latvian 20th seed Jelena Ostapenko or Bernarda Pera of the United States.

On Friday's form, Swiatek will take some stopping if she is to be denied a place in the quarter-finals.

The 22-year-old from Warsaw was utterly ruthless from the outset against Juvan, racing through the first set in just 24 minutes after four straight breaks of serve.

She kept up the barrage in the second set, reeling off 13 straight points on the way to opening up a 3-0 lead.

Juvan earned some well-deserved applause by holding her serve to make it 3-1, but the respite was fleeting.

Swiatek held and then broke Juvan again for a 5-1 lead before easily holding to complete a quickfire win.

rcw/mw