The 22-year-old, ranked world No. 1 by the Women's Tennis Association (WTA), saw off Chinese player Wang Xiyu 6-1, 6-4 in their second-round encounter on Thursday.
Up next for the Polish player at the clay-court tournament in the Spanish capital is 27th seed Sorana Cîrstea of Romania.
Świątek in March won the BNP Paribas Open tournament at Indian Wells, California, claiming her 19th career singles title.
The Polish star in November regained her spot at the top of the world rankings in women's tennis after winning the season-ending WTA Finals tournament in Mexico.
The Pole, coached by countryman Tomasz Wiktorowski, leads the WTA rankings with 10,560 points, ahead of Belarusian Aryna Sabalenka, with 7,848 points, and American Coco Gauff, with 7,258.
(gs)
Source: PAP