Stefanos Tsitsipas and Maria Sakkari of Greece during their United Cup tennis mixed doubles match against Sergio Martos Gornes and Yvonne Cavalle-Reimers of Spain, in Perth, Australia.

Sergio Martos Gornes and Yvonne Cavalle-Reimers of Spain during their United Cup tennis mixed doubles match against Stefanos Tsitsipas and Maria Sakkari of Greece, in Perth, Australia.

Stefanos Tsitsipas and Maria Sakkari of Greece during their United Cup tennis mixed doubles match against Sergio Martos Gornes and Yvonne Cavalle-Reimers of Spain, in Perth, Australia.

Sergio Martos Gornes and Yvonne Cavalle-Reimers of Spain during their United Cup tennis mixed doubles match against Stefanos Tsitsipas and Maria Sakkari of Greece, in Perth, Australia.

Sergio Martos Gornes and Yvonne Cavalle-Reimers of Spain talk between points during their United Cup tennis mixed doubles match against Stefanos Tsitsipas and Maria Sakkari of Greece, in Perth, Australia.

Stefanos Tsitsipas of Greece, right, shakes hands at the net after defeating Pablo Carreno Busta of Spain in their United Cup tennis match in Perth, Australia.

Stefanos Tsitsipas of Greece reacts after winning a crucial point over Pablo Carreno Busta of Spain during their United Cup tennis match in Perth, Australia.

Pablo Carreno Busta of Spain hits a return shot to Stefanos Tsitsipas of Greece during their United Cup tennis match in Perth, Australia.

Stefanos Tsitsipas of Greece hits a return shot to Pablo Carreno Busta of Spain during their United Cup tennis match in Perth, Australia.

Stefanos Tsitsipas of Greece serves to Pablo Carreno Busta of Spain during their United Cup tennis match in Perth, Australia.