New York, Aug 31 (AFP) Top-ranked defending champion Novak Djokovic rolled into the US Open fourth round while Serena Williams and Roger Federer cruised into the last 16 and Kei Nishikori was eliminated.

Djokovic, champion in four of the past five Slams and 16 overall, was less bothered by left shoulder pain that nagged him in the second round in defeating 111th-ranked American Denis Kudla 6-3, 6-4, 6-2 on Friday.

"That I managed to play almost pain-free, that's a big improvement from last match obviously," Djokovic said.

"I didn't know how my body would react. That was nice." Djokovic, who needed treatment throughout his second-round triumph, skipped practice Thursday in favour of shoulder treatment.

"I'm not going to go into the medical details," he said.

"But it definitely was bothering me in the past couple weeks."

The 32-year-old Serbian, a three-time US Open winner, booked a Sunday showdown with three-time Slam winner Stan Wawrinka, the Swiss 23rd seed who eliminated Italian lucky loser Paolo Lorenzi 6-4, 7-6 (11/9), 7-6 (7/4).

"There's something with him that when I get into my best game, I know that it's going to have some big rallies and I'm going to play good tennis," Wawrinka said.

Djokovic, no worse than a US Open semi-finalist since a third-round exit in 2006, leads Wawrinka 19-5 in their all-time rivalry, but they haven't met since Wawrinka beat Djokovic in the 2016 US Open final.

"We've had some great battles over the years, but especially here," Djokovic said.

"He's a three-time Grand Slam champion, someone that possesses a game with a lot of power, a lot of quality. Let the better player win."

Federer routed Britain's 58th-ranked Dan Evans 6-2, 6-2, 6-1 in only 80 minutes, blasting 48 winners to just seven for Evans. After dropping the first set in his first two matches, the 20-time Grand Slam champion was solid from start to finish.

"What matters the most is that I'm in the third round after those two sort of slow starts," Federer said.

"I actually can go through three sets in a row playing really good tennis."

Evans blasted organizers for giving him short rest after a rain-delayed match while his 38-year-old Swiss rival rested after playing Wednesday under the roof at Arthur Ashe Stadium.

"I actually thought he played pretty much no-error tennis," Evans said. Next up for Federer is Belgian 15th seed David Goffin.

- De Minaur causes upset -

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Williams continued her quest for a 24th career Grand Slam title to equal Margaret Court's all-time record by crushing 44th-ranked Czech Karolina Muchova 6-3, 6-2 in 74 minutes.

"I had a lot of intensity today, which is really good for me," said Williams, whose next opponent is Croatian 22nd seed Petra Martic.

The 37-year-old American, a six-time US Open champion, last won a Slam at the 2017 Australian Open and hasn't won the US Open since 2014.

Japanese seventh seed Nishikori, the 2014 US Open runner-up, lost to Australia's Alex de Minaur 6-2, 6-4, 2-6, 6-3. The 20-year-old Aussie, on his deepest Grand Slam run, took his first victory over a top-10 foe in 12 tries.

"This is where I feel like my game's at. I want to be pushing second weeks of Grand Slams and putting myself out there. So very happy," De Minaur said.

"Hopefully I can just keep it rolling." De Minaur faces Bulgaria's Grigor Dimitrov next.

Reigning French Open champion Ashleigh Barty, the Aussie second seed, and Czech third seed Karolina Pliskova, chasing her first Slam title, also advanced.

Pliskova, the 2016 US Open runner-up, outlasted Tunisia's Ons Jabeur 6-1, 4-6, 6-4 while Barty dispatched Greek 30th seed Maria Sakkari 7-5, 6-3.

"Physically it was quite a tough battle," Pliskova said. "So pleased to be through."

Pliskova next plays British 16th seed Johanna Konta while Barty, a possible Williams quarter-final foe, meets Chinese 18th seed Wang Qiang.

"It's going to be an incredibly physical match," Barty said.

"I need to make sure I serve well and bring variety in as much as I can."

Barty and Pliskova are battling top-ranked defending champion Naomi Osaka to be world number one at the end of the Flushing Meadows fortnight.

One more Barty win would ensure Japan's Osaka is dethroned but Pliskova could still take the top spot by reaching the final.

Also advancing was Ukrainian fifth seed and Wimbledon semi-finalist Elina Svitolina, who next faces US 10th seed Madison Keys, a 6-3, 7-5 winner over compatriot Sofia Kenin. (AFP)

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