The top-ranked Serb never gave Nishikori a chance in a 6-2, 6-0 rout of the home favorite from Japan to reach the semifinals of the tennis tournament at the Tokyo Olympics on Thursday.
"He was defending amazing today -- everything deep -- and I was trying to stay with him but I couldn't," Nishikori said. "I thought I was playing OK but my serving was bad today and he was attacking every [time]."
The dominant performance advanced Djokovic into the medal rounds and -- more importantly -- moved him one step closer to finishing off this segment of his Golden Slam bid.
Djokovic -- who is in his third Olympic semifinal but has never made it to the gold-medal match -- will next face either Alexander Zverev of Germany or Jeremy Chardy of France. The other semifinal will feature Karen Khachanov of ROC against Pablo Carreno Busta of Spain.
Djokovic, who has already won the Australian Open, French Open and Wimbledon this year, needs the Tokyo Games title and the US Open trophy to become the first man to achieve the Golden Slam.
"The way he's played today, this week and last couple months, it's been amazing," Nishikori said.
As it's been for months, it seems that Djokovic, who has not dropped a set in the tournament, is getting better match by match -- so much so that it looks like he's hardly being tested.
"Matches are not getting easier, but my level of tennis is getting better and better and and I've done that so many times in my career," Djokovic said. "I'm [the] kind of player that the further the tournament goes the better I'm feeling on the court and that's the case here."
Over the course of the match, there was really only one moment when Djokovic was in slight trouble. It came in the opening game of the second set when Nishikori held a break point. Djokovic responded with a rally that sent Nishikori scrambling from corner to corner before unleashing a forehand crosscourt winner that the Nishikori couldn't come close to getting his racket on. That prompted a loud roar from Djokovic
After it was done, Djokovic called it his "best performance" of the tournament.
"Against [a] very good opponent," he said. "I felt like I had an answer for everything he had."
For the second straight day, Djokovic had two matches scheduled. He's also playing again later with Serbian partner Nina Stojanovic against the German pair of Laura Siegemund and Kevin Krawietz in the mixed doubles quarterfinals.
Bencic also had another match scheduled. She was scheduled to play with Swiss partner Viktorija Golubic against the Brazilian pair of Laura Pigossi and Luisa Stefani in the semifinals of the doubles tournament.
"To have the medal for me is the greatest thing," Bencic said of her singles play. "Now I go to the doubles and I hope to do it again so it's not over yet, but I can really, really enjoy this moment."
If she also wins in doubles, Bencic would become the fifth player to reach two finals at the same Olympics since tennis returned at the Games in 1988, joining Serena and Venus Williams, Andy Murray and Nicolas Massu.
"In the next match I can be more relaxed because I already have a medal," Bencic said.
The results means that Switzerland is guaranteed a tennis medal at a fourth consecutive Olympics after Roger Federer and Stan Wawrinka won gold in doubles in 2008, Federer took silver in singles in 2012 and Martina Hingis and Timea Bacsinszky claimed silver in doubles in 2016.
Federer announced a week before the Tokyo Games began that he wouldn't play at the Olympics because he "experienced a setback" with his knee during the grass-court season. That left Bencic as Switzerland's most accomplished player in Tokyo and her performance represents a personal breakthrough for someone whose best Grand Slam result was reaching the semifinals at the 2019 U.S. Open.
Play started four hours later than on previous days after organizers finally acted upon a request from players to avoid the hottest part of the day.
"Playing after after 5:00 is completely different," Djokovic said. "Still very, very humid, you sweat a lot, but you don't have the heat, you don't have the sun in combination with the humidity."