Fantasy Mixed Doubles 2013: Top Eight Teams

The tennis calendar for both the ATP and the WTA tours are finally over for 2013 so it's the time of year where I play my own fantasy tennis using this week's rankings of both tours.
The first fantasy tournament involves a 'Hopman'-like Cup where a country is composed of one male and one female player and both will play singles and doubles.
Here are the countries that qualified this year and their group assignments:


GROUP A


SERBIA
Novak Djokovic
Jelena Jankovic

UNITED STATES
John Isner
Serena Williams 

RUSSIA
Mikhail Youzhny
Maria Sharapova

GERMANY
Tommy Haas
Angelique Kerber



GROUP B

CZECH REPUBLIC 
Tomas Berdych
Petra Kvitova 

SPAIN
Rafael Nadal
Carla Suarez Navarro


ITALY
Fabio Fognini
Sara Errani


POLAND
Jerzy Janowicz
Agnieszka Radwanska