Swiatek advances to face in-form Ukrainian Marta Kostyuk, who is unbeaten in 14 matches on clay this season following titles in Madrid and Rouen.
Third seed Swiatek dug herself out of an early 2-0 hole against her 35th-ranked opponent, who won their most recent meeting at Miami in March.
Swiatek broke three times in the opening set to nose ahead, and then surged into a 4-1 lead in the second set.
She overcame a stumble as she tried to close it out, before wrapping up victory in one hour and 25 minutes on another hot day at Roland Garros.
Kostyuk, the 15th seed, continued her fine run earlier with a 6-4, 6-3 win over Switzerland's Viktorija Golubic.
