Novak Djokovic will play Japan's Kei Nishikori in the quarter-finals of the Tokyo Olympics after the world number one breezed past Alejandro Davidovich Fokina in straight sets on Wednesday.

Djokovic continued his bid for a calendar Golden Slam by defeating the 34th-ranked Spaniard 6-3, 6-1 to extend his winning run to 21 matches.

The Serb, a bronze medallist in 2008, is trying to emulate Steffi Graf's 1988 feat of winning Olympic gold and all four Grand Slams in the same year.