Świątek and Mattek-Sands had been seeded 14th in the tournament to Krejčíková and Siniaková's 2nd.
The Czech duo had defeated Poland's Magda Linette and America's Bernarda Pera 6-1, 6-2 in the semi-finals in Paris on Friday.
Last Wednesday, Iga Świątek's hopes of defending her title at the French Open failed as she lost in the quarter finals of the women's singles to Greece's Maria Sakkari. Barbora Krejčíková took the title at Roland Garros, on Saturday defeating Anastasia Pavlyuchenkova 6:1, 2:6, 6:4.
Source: PAP