The world number one, chasing a calendar Golden Grand Slam, ended home interest in the tennis with a ruthless 6-2, 6-0 victory in only 70 minutes.

Djokovic has never won the Olympic singles title, with a bronze medal in 2008 his best result at the Games, but will face either Alexander Zverev or Jeremy Chardy in the last four.

The 34-year-old Serb, who has already captured the Australian Open, French Open and Wimbledon titles this season, was never in trouble against Nishikori, who made 16 unforced errors.

The former world number four did save two match points in the final game, but Djokovic made no mistake on the next opportunity.

The quarter-final was played in cooler conditions than earlier in the tournament after Djokovic lobbied organisers to change the schedule, moving the day's start time from 11:00 am local time (0200 GMT) to 3:00 pm.

Djokovic is also in action later Thursday in the mixed doubles quarter-finals alongside Nina Stojanovic, facing Germany's Kevin Krawietz and Laura Siegemund.