Defending champion Novak Djokovic is through to the US Open last 16 after showing few signs of a shoulder injury in a straight-set victory over American Denis Kudla.

The top seed progressed with a 6-3 6-4 6-2 win against the 111th-ranked Kudla.

The Serb, 32, has been struggling with the problem for “a couple of weeks”, but said he was “almost pain free”.

“That’s a big improvement on my last match,” said Djokovic, who will play Swiss 23rd seed Stan Wawrinka next.

The three-time US Open champion is the favourite to win his fifth Grand Slam from the past six, but was hampered by the shoulder problem during his second-round victory over Argentina’s Juan Ignacio Londero – needing three medical time-outs during Wednesday’s match.

Afterwards, he said he would need to use his day off on Thursday to have more treatment to put him in “a better state” for Friday’s final match on Arthur Ashe Stadium, and did not practise at Flushing Meadows until about 19:45 local time, before going on court under two hours later.

Yet he encountered few problems against Kudla, breaking serve four times and saving seven break points to set up a meeting with three-time Grand Slam champion Wawrinka – who is likely to push Djokovic more physically – on Sunday.

Wawrinka, 34, beat Djokovic at Flushing Meadows to win the 2016 title.

Djokovic was involved in an incident during his practice on Friday, in which he said to a fan, in a video shared on social media, “I’ll find you afterwards, I’ll come find you”.

Speaking after his match, the Serb laughed off the incident, saying the pair “just had a little chat” and explained he wanted to find the fan “to buy him a drink”.

Asked what was he said, he replied: “We’ll keep it between us. But he definitely helped me. He doesn’t even know, but he did help me.

“Even maybe he didn’t want to do me a favour, he did me a favour, big favour.”

Medvedev overcomes Lopez and boos

Russian fifth seed Daniil Medvedev was booed by a hostile crowd as he beat Spanish veteran Feliciano Lopez 7-6 (7-1) 4-6 7-6 (9-7) 6-4 on Louis Armstrong Stadium.

The world number five received an unsportsmanlike conduct code violation for snatching a towel from a ballperson’s hands in the first set, and he later made an offensive gesture towards the crowd.

He escaped punishment for the gesture, unseen by the umpire despite it being replayed on a television screen in the stadium, as umpire Damien Dumusois said he would “have to see it myself.”

Medvedev was also booed as he was interviewed on court after the match, and said: “I want all of you to know, when you sleep tonight, I won because of you. The energy you gave. The more you do this, the more I win.”

He faces German qualifier Dominik Koepfer next and said he would try and improve his behaviour.

“I am working on myself and hopefully I will be better next time,” added the Russian.

Nishikori downed by De Minaur

Seventh seed Kei Nishikori is out after losing to 20-year-old Australian Alex de Minaur.

The Japanese, runner-up at Flushing Meadows in 2014, went two sets down before a brief fightback in a 6-2 6-4 2-6 6-3 defeat.

For Australian world number 38 De Minaur, one of the game’s rising stars, it was his first win over a top-10 player and he will face Bulgarian Grigor Dimitrov next.

“This is where I feel like my game’s at,” De Minaur said after reaching the last 16 of a Grand Slam for the first time.

“I want to be pushing second weeks of Grand Slams and putting myself out there. So very happy. Hopefully I can just keep it rolling.”

In 2018 at the same venue, the Australian squandered a two-set lead against 2014 champion Marin Cilic to lose in five sets in the third round.

“Last year it was a bit of a heartbreaking match for me,” he said. “It stung a lot, but you learn so much from it. You know that that’s your level.”

Meanwhile, Belgium’s David Goffin beat Spaniard Pablo Carreno-Busta 7-6 (7-5) 7-6 (11-9) 7-5 and will next take on 20-time Grand Slam champion Roger Federer, who knocked out Briton Dan Evans.

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