The Polish duo on Wednesday defeated France's Fiona Ferro and Pierre-Hugues Herbert 6-3, 7-6 in their first-round match in the Japanese capital.
Photo: PAP/Leszek Szymański
Świątek and Kubot will now face Elena Vesnina and Aslan Karatsev of the Russian Olympic Committee for a place in the semifinals.
In the first round, Vesnina and Karatsev dispatched the top-seeded French team of Nicolas Mahut and Kristina Mladenovic, winning 6-4, 6-2.
Poland's Świątek on Monday crashed out of the women's singles competition in Tokyo, after losing 3-6 6-7 to Paula Badosa of Spain in the second round.
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Source: PAP, Eurosport