Novak Djokovic and Roger Federer remain on a collision course to meet in the US Open semi-finals after they each claimed straight-sets wins to reach the last 16.

Djokovic declared himself "almost pain-free" after coming through a decent test from Denis Kudla and sealing a meeting with Stan Wawrinka, the defending champion having faced questions about his troublesome left shoulder going into his 6-3 6-4 6-2 victory.

Federer has had no such fitness issues and breezed through against Daniel Evans, though the Swiss was forced to respond to suggestions he had influenced the decision to have him play first on Arthur Ashe against the Briton, who had come through a four-set encounter on Thursday.

Next for Federer is David Goffin after the Belgian overcame Pablo Carreno Busta in three sets.

Daniil Medvedev provided late drama in the last match on Louis Armstrong, with his victory over Feliciano Lopez booed by fans after he was seen to aim a middle finger at them.

MEDVEDEV WINS DESPITE MELTDOWN

World number five Medvedev needed three hours and 19 minutes to see off Lopez 7-6 (7-1) 4-6 7-6 (9-7) 6-4, the Russian progressing despite a first-set meltdown.

Medvedev lost all support from the crowd after he was seen to direct an insulting gesture at them, this after he had been assessed a code violation for snatching a towel from a ball boy, which he reacted to by tossing a racquet in the direction of the umpire's chair.

The Russian revelled in the boos that came after he clinched victory, seemingly enjoying playing the role of villain, telling the crowd their energy will be "enough for the next five matches".

He later described his actions as "heat of the moment" and expressed hope he will deal with such situations better next time. Whether he will have the crowd on side in his match with qualifier Dominik Koepfer, who is set to break into the top 100 after beating 17th seed Nikoloz Basilashvili in four sets, is debatable at best.

WAWRINKA EXPECTS TO BRING HIS BEST

Wawrinka has beaten Djokovic twice in grand slam finals, at the French Open and in New York, and anticipates producing his best tennis against the world number one in round four.

The Swiss saw off Paolo Lorenzi in three sets, a day after the Italian completed a second-round match that lasted nearly five hours.

Speaking in a media conference, Wawrinka said of his meeting with Djokovic: "There's something with him that when I get into my best game, I know that it's going to have some big rally, I'm going to play good tennis."

DEMON DE MINAUR SET FOR DIMITROV DUEL

Alex de Minaur claimed his first top-10 win as he shocked seventh seed Kei Nishikori 6-2 6-4 2-6 6-3. 

The Australian was afterwards asked if he had a nickname he likes and replied: "Demon. That's something that's sort of caught on in Australia. And, yeah, I don't mind it.

"I like to think it's got something to do with sort of my fiery attitude on court. Just, you know, I get pretty fired up and pumped up. I'd like to think it's something to do with that."

Grigor Dimitrov will be the next man faced with De Minaur's fire, after the Bulgarian saw off Kamil Majchrzak in three sets.