US Open: Novak Djokovic moves four wins away from a calendar Grand Slam and 21st major

Novak Djokovic moved four wins away from a calendar Grand Slam and 21st major thanks to a 17th straight win over Kei Nishikori at the US Open.

Not since a semi-final win over the great Serbian in New York in 2014 had Nishikori got the better of Djokovic, and he won just two games at the Olympics in Tokyo earlier this summer.

Nishikori won the first set in Arthur Ashe Stadium to threaten a huge upset but Djokovic roared his way to a 6-7 (4-7) 6-3 6-3 6-2 victory and a place in the fourth round.

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The top seed said: "I don't think I started off very well, I was quite passive. I was still trying to find the rhythm. Obviously, he played much quicker and more aggressive than my opponents in the first two rounds.

"In the beginning of the second set, I already felt like I was getting the groove back. I was very pleased with the focus. Maybe at some points I wasn't at my best but overall I was determined, I was concentrated, and that's what matters in the end."

A tight opening set was snatched by Nishikori in a tiebreak before Djokovic began to settle into the contest, breaking the Japanese player twice in the second on his way to levelling the match at a set apiece.

In another workmanlike effort, the top seed took the decisive break in the third to go ahead 5-3 then held serve for a 2-1 lead.

Now in control, Djokovic would leave Nishikori no openings to hope for a comeback, storming through the last four games of the fourth set to close out the contest in style.

The Serbian now face 20-year-old Jenson Brooksby after the American wildcard shocked Russian Aslan Karatsev 6-2 3-6 2-6 6-3 6-3.

Fourth seed Alexander Zverev booked his spot in the fourth round after Jack Sock retired in the fourth set of their match on Arthur Ashe.

Sock won the first set, but received treatment early in the second and had to call time with Zverev winning 3-6 6-2 6-3 2-1.

Zverev said on court: "If Jack had kept on playing the way he was doing in the first set, I would have been done in an hour and a half and been planning my holidays and having a good time next week somewhere in the south of France."

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Sixth seed Matteo Berrettini survived a third-round test from Ilya Ivashka to win 6-7 (5-7) 6-2 6-4 2-6 6-3, firing off 27 aces in front of an adoring Grandstand crowd.

In the last 16, the Italian will face one of the tournament's surprise packages in German Oscar Otte, who showed his talents in a five-set battle with Andy Murray at Wimbledon and progressed after a four-set win over Andreas Seppi.

Jannik Sinner came through a gruelling five-setter against Frenchman Gael Monfils, winning 7-6 (7-1) 6-2 4-6 4-6 6-4 to reach the last 16 for the first time.

Monfils delighted the crowd by battling from 4-0 down in the fourth set to force a decider but Sinner again showed his competitive toughness by coming out on top.

Seventh seed and 2020 quarter-finalist Denis Shapovalov crashed out to South African Lloyd Harris, going down to a surprise 6-4 6-4 6-4 defeat.

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