They beat eighth seeds Julia Goerges of Germany and Nenad Zimonjic of Serbia 4-6 6-2 10-7 in the final.
Groenefeld won the mixed doubles title at Wimbledon in 2009 with Mark Knowles of the Bahamas.
Rojer reached the Wimbledon semi-finals last year with Russian Vera Dushevina.
(Reporting by Alison Williams, editing by Ed Osmond)
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