The result shattered the hopes of the South American pair who only teamed up after Schwank's original partner Horacio Zeballos pulled out injured.
Had they triumphed, Cabal would have been the first man to win a major title on his debut appearance.
But the greater experience of second seeds Mirnyi and Nestor eventually told as they won their first major title as a team.
With different partners, Mirnyi had already won four grand slam titles and Nestor six.
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