Novak Djokovic beats Tomas ##si in a third - set tie - break in Group B opener . Serbian saves a match point to win at the season - ending championships . Fifth seed David Ferrer upsets home favourite Andy Murray in Monday 's first game . World No . 3 Murray plays with groin injury and may miss the tournament .
Novak Djokovic beats Tomas Berdych in a third-set tie-break in Group A opener . Serbian saves a match point to triumph at the season-ending championships . Fifth seed David Ferrer upsets home hope Andy Murray in Monday 's first game . World No . 3 Murray struggling with groin injury and may quit the tournament .