|US Open 2021|
|Venue: Flushing Meadows, New York Date: 30 August-12 September|
|Coverage: Daily radio commentaries on BBC Radio 5 Live Sports Extra/BBC Sport website and app, with selected live text commentaries and match reports on the website and app|
Novak Djokovic had to come from behind to beat Kei Nishikori and keep his bid for a calendar Grand Slam alive as he advanced to the US Open fourth round.
The world number one overcame a loose first set to win 6-7 (4-7) 6-3 6-3 6-2 and beat the Japanese for the 17th time in a row.
The Serb, 34, is aiming for a men's record 21st Grand Slam title.
He will face American Jenson Brooksby next, after the wildcard beat Russian 21st seed Aslan Karatsev in five sets.
Brooksby, the world number 99, came from behind to win 6-2 3-6 2-6 6-3 6-3 and become the youngest man from the USA to reach the US Open fourth round since Andy Roddick in 2002.
Top seed Djokovic has received a mixed reception from the New York crowd but appeared to have won them over by the final point.
He asked them to give him more noise several times, cupping his ear toward the fans, and did not do his traditional 'show of love' celebration to the stands.
He did, however, spend some time after his post-match interview signing autographs and giving several young fans items from his kit bag.
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Djokovic looked out of sorts in the opening set, although he battled back from an early break down to force a tie-break.
However, he struggled with his serve, and Nishikori took full advantage to take just his fourth set off Djokovic out of the past 33 they have played.
Nishikori fought hard but was only able to convert two of the 13 break-point opportunities he created.
One of those breaks came as Djokovic served for a 5-3 lead in the third set, but the Serb instantly hit back and cruised through a routine fourth to close out the match.
"I don't think I started off very well but he surprised me with his level today," Djokovic said.
"It took me a little bit of time to adjust to his game."
German qualifier Oscar Otte reached the fourth round of a Grand Slam for the first time with victory over Italy's Andrea Seppi.
World number 114 Otte, who was match point down in his first two qualifying matches, won 6-3 6-4 2-6 7-5.
He will face Wimbledon finalist Matteo Berrettini, who had to work hard to see off Belarusian Ilya Ivashka.
The Italian sixth seed hit 69 winners as he came through 6-7 (5-7) 6-2 6-4 2-6 6-3.
Italian 13th seed Jannik Sinner overcame Gael Monfils in five sets, weathering a fightback from the Frenchman to win 7-6 (7-1) 6-2 4-6 4-6 6-4.
Sinner will meet German fourth seed Alexander Zverev who advanced after opponent Jack Sock retired with a thigh injury trailing 3-6 6-2 6-3 2-1.
The American had convincingly won the first set but began to suffer injury problems from the beginning of the second. After being broken in the fourth set he eventually gave up, knowing there was no way back.
South Africa's Lloyd Harris continued his good form with a 6-4 6-4 6-4 win over Canada's Wimbledon semi-finalist Denis Shapovalov.
He will play Reilly Opelka next after the American beat Nikoloz Basilashvili of Georgia 7-6 (7-5) 6-3 6-4.
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