Rafael Nadal allayed fears over his knee and believes he will be stronger for the four-hour examination he came through against Karen Khachanov at Flushing Meadows.

The 22-year-old Russian, who stands 6ft 6in and has a game to match, won the opening set of the third-round clash and served for the second but Nadal's well of resilience rarely runs dry and he fought back to win 5-7 7-5 7-6 (9/7) 7-6 (7/3).

The defending champion made some unusual errors even when he seemed to be in control, letting a 6-3 lead slip in the third-set tie-break before eventually winning it and then being broken to love when he served for the match at 5-4 in the fourth.

He said: "I went through some very difficult situations. But he played well. He's improving always. He's young. He has everything. He's a great player. I really see him winning a lot of matches in his tennis career.

"I believe that there is some margin (for me) to improve. But I really hope that this kind of match helps. These kind of matches make you feel confident, make you feel stronger. At some point you need to go through some tough moments."

The most alarming moment for Nadal fans came at the end of the first set when he had his right knee taped.
Given his history of knee trouble, it is always a worrying sign, but the Spaniard insisted he expects to be fully fit for his fourth-round clash with Georgia's Nikoloz Basilashvili.

"It was just something that I felt, but I try always during the tournaments not to speak much about these kind of things," said Nadal. "But my personal feeling is I'm going to be at my 100% for the next one."

After breaking Nadal for the second time in the opening set to lead 6-5, Khachanov withstood an onslaught from his opponent to serve it out.

The Russian then opened up an early lead in the second set and had a chance to serve for that one too.
But back came Nadal and, after a short rain break during which the roof was closed on Arthur Ashe Stadium, he made it three games in a row to take the set, celebrating with a leaping double fist-pump.

Nadal said: "I was just trying to calm myself for a moment. For me, the most important thing is have the right tempo when I am playing. For some moments I felt things were going too fast in my mind.

"I didn't take the time to do the right steps, to go to the ball with the right decision, with the right determination, with the right timing."

Any thoughts that Nadal would run away with the match were swiftly put aside as Khachanov kept pace through to a third-set tie-break.

Nadal seemed certain to take it when he led 6-3 only to make two errors and be denied by good play from Khachanov. The Spaniard eventually edged it on a 39-shot rally, with three double faults from his opponent proving particularly costly.

Nadal did finally have some control at the start of the fourth set but, trying to serve out the match, the nerves kicked in.

Khachanov went for broke, and the Russian took the game to love. He held one set point two games later but netted a backhand and that was to prove his final chance.

Khachanov said: "I gave everything I had. I think everybody saw it. I'm proud of myself that I could play a good game today, fight until the end. Just a few points difference and it could go another way.

"Big respect to Rafa. That's why he's number one in the world, such a great fighter. I'm just happy about my performance. To see the level I can play. That just shows that I'm really close to this high level against top guys. Hopefully it will be soon on my side."

Kevin Anderson, the man Nadal beat in the final 12 months ago, also survived a severe test, defeating 19-year-old Denis Shapovalov 4-6 6-3 6-4 4-6 6-4. He next faces ninth seed Dominic Thiem, who beat Taylor Fritz 3-6 6-3 7-6 (7/5) 6-4.

2016 champion Stan Wawrinka was on a nine-match winning streak at Flushing Meadows, having missed the tournament 12 months ago following knee surgery, but his run was ended by Milos Raonic.

Raonic, the 25th seed, has been showing much-improved form this summer after his own injury struggles and impressed in a 7-6 (8/6) 6-4 6-3 victory to set up a fourth-round clash with John Isner.

The pair also met at Wimbledon, with Isner coming out on top. The American was a 7-6 (10/8) 6-7 (6/8) 6-3 7-5 winner against Dusan Lajovic.