Novak Djokovic sees off Kei Nishikori, Maria Sharapova reaches last 16 in Madrid

Former world number one Novak Djokovic's bid for a third Madrid Open title began with a 7-5 6-4 first-round win over Kei Nishikori.

The Japanese had reached the quarter-finals or better in each of the last five years but lost a first set littered with mistakes.