Novak Djokovic beats John Isner in eight -set marathon as Spain beat USA in the Davis Cup tie . Serbia reach quarterfinals of the World Group for the third time . Defending champions Spain will play France in pick of the last five ties .
Novak Djokovic beats John Isner in five-set marathon as Serbia beat USA in Davis Cup tie . Serbia reach quarterfinals of the World Group for the first time . Defending champions Spain will play France in pick of the last eight ties .