The Polish world No. 1 was leading 6-1, 2-6, 4-1 when the ninth-ranked American retired in the third set due to an injury.
The 23-year-old Pole, who last month won her fourth French Open title in Paris, will now face Qinwen Zheng of China for a place in the Olympic final.
Świątek has expressed her desire to win Olympic gold this year, bolstered by the fact that the tournament is being held on her favourite clay surface.
She hopes to make amends in Paris after an unsuccessful campaign in Tokyo. Many consider her the country's best chance for a gold medal at the 2024 Games.
Świątek is the last Pole standing in the Olympic tennis tournament in Paris.
(gs)
Source: TVP, IAR, PAP