World number one Swiatek reached the US Open last 16 with a dominant straight-set victory over Slovenia's Juvan.
The pair have known each other since they were teenagers but Swiatek was ruthless in a 6-0 6-1 win, making only one unforced error in the first set and dropping 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."
After winning the first set in 24 minutes, Swiatek raced out to a 3-0 lead in the second.
When Juvan finally won the next game to ensure she avoided a dreaded 'double bagel' she waved her arms and looked up to the sky in relief, with the crowd loudly cheering her on.
Swiatek, however, remained completely focused, winning the next three games to clinch the match before the pair shared a warm embrace at the net.
Swiatek will play Jelena Ostapenko, who she has not beaten in three attempts, after the Latvian 20th seed fought back to beat American Bernarda Pera 4-6 6-3 6-3.
Elsewhere on Friday, 10th seed Muchova beat American Taylor Townsend 7-6 (7-0) 6-3 to set up a fourth round meeting with China's Wang Xinyu.
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