Match detailsFixture: (1) Novak Djokovic vs Kei NishikoriDate: 4 September 2021Tournament: 2021 US OpenRound: Third round (Round of 32)Venue: Flushing Meadows, New YorkCategory: Grand SlamSurface: Outdoor hardcourtPrize money: $40,560,000Live telecast: USA - Tennis Channel & ESPN/ESPN 2 | UK - Amazon Prime Video | India - Star Sports / Disney+ Hotstar VIPNovak Djokovic vs Kei Nishikori previewNovak Djokovic will meet familiar foe Kei Nishikori in the third round of the 2021 US Open on Saturday.Djokovic defeated Tallon Griekspoor 6-2, 6-3, 6-2 in his second-round match on Thursday. The Serb was not at his imperious best but showed some improvement from his first-round match against Holger Rune.Djokovic struck 33 winners, including 13 aces, to keep his hopes of the Calendar Slam alive. The 20-time Major champion also won 80% of his first-serve points and broke Griekspoor as many as six times.The quest for 21 has begun.@DjokerNole takes the court in Ashe. #USOpen pic.twitter.com/uj2bvjzo42— US Open Tennis (@usopen) August 31, 2021While Djokovic did get broken once, he didn't give much leeway to his opponent in the other games. The Dutchman could manage a meager 29% win rate while returning.That said, Djokovic would want to reduce his unforced error count as the tournament progresses. He coughed up 20 unforced errors on Thursday, out of which five were double faults.Kei Nishikori, meanwhile, registered a closely-fought win over America's Mackenzie McDonald in his second-round fixture. Nishikori led by two sets to love but lost his way as Mcdonald leveled the match with some tremendous counterpunching. But the Japanese pulled up his socks in the decider to come out on top with a 7-6(3), 6-3, 6-7(5), 2-6, 6-3 scoreline.Kei Nishikori will have his task cut out against Novak DjokovicNishikori spent nearly four hours on the court, during which he struck 45 winners while making 57 unforced errors. Interestingly, McDonald hit the same number of winners and committed three fewer unforced errors.The two players broke the other's serve eight times each, indicating the closeness of the affair. What tilted the scales in Nishikori's favor was that he landed more first serves in the decider, while also conjuring up almost twice the number of winners as his counterpart.Novak Djokovic vs Kei Nishikori head-to-head2014 semifinal: Nishikori2018 semifinal: DjokovicWho will take the #USOpen rubber match? pic.twitter.com/5pGo05w4AH— US Open Tennis (@usopen) September 3, 2021Novak Djokovic leads Kei Nishikori by a whopping margin of 17-2 in the head-to-head. Nishikori has, however, beaten the Serb at the US Open before; the Japanese won a four-set semifinal at the 2014 US Open.Since then, Djokovic has registered 16 straight victories against Nishikori, including one at the recent Tokyo Olympics.Novak Djokovic vs Kei Nishikori predictionStyle-wise, Kei Nishikori is somewhat similar to Novak Djokovic. Both players are incredible athletes and returners, and boast remarkable accuracy on their groundstrokes. They also excel at redirecting pace.But Djokovic is a cut above the Japanese, for he knows exactly when to take the pace off the ball and when to pull the trigger.Nishikori doesn't enjoy much success in this matchup because the Serb often feasts on his serve, which isn't amongst the best in the business. And given how well Djokovic has been serving lately, it looks unlikely that the 2014 US Open runner-up will get anything out of this contest.Prediction: Novak Djokovic to win in straight sets.