The world's top three players, with 53 grand slams between them, all had the easiest of afternoons on Monday, dropping just 19 games across their three matches.

Nadal will face Sam Querrey in the quarter-finals after the American beat Tennys Sandgren 6-4, 6-7 (7-9), 7-6 (7-3), 7-6 (7-5).

While Nadal was not troubled by Sousa, he was embroiled in a debate over scheduling, with reporters questioning why he was on Centre Court when women's top seed Ashleigh Barty was on the Court Two outpost.

Despite her status, the French Open champion played only one of her four Wimbledon matches on Centre Court this year.

Barty was even shunted to Court 2, the third-ranked court at the All England Club, for two rounds - including Monday's loss to American Alison Riske.

"I am the world No.2 and I won 18 grand slams," Nadal said.

"My answer is not no or yes. My answer is they make a decision.

"You are putting Ashleigh Barty in front of me. For me, both decisions are good."

Barty typically wasn't fussed about where she played on, sticking to her party line that all courts at Wimbledon were beautiful.

"Scheduling is out of my control," she said.

"I'll play on any court I'm scheduled on."

Djokovic beat French rookie Ugo Humbert 6-3, 6-2, 6-3 as their dominance of the game was laid bare.

Federer posted the fastest ever fourth-round win at Wimbledon, beating Matteo Berrettini 6-1, 6-2, 6-2 in 74 minutes while Nadal beat Joao Sousa 6-2, 6-2, 6-2.

The champion this year looks sure to be one of those three men as the next generation of players struggle to get anywhere near them on the biggest stage.

Asked why that continues to be the case, Djokovic said: "I have no explanation for that. I leave it to you to understand why.

"I think we are working as hard as anybody really to be there.

"It's great that I'm one of these three guys and still very successful.

"We talked about it many times, of course, that you see new faces in sport.

"Young guys will eventually replace us at the top spots of the world. This is going to happen? When? Hopefully not too soon, but it's going to happen.

Even Federer was surprised at just how easy his 99th SW19 victory was.

"Obviously today was excellent. I was very happy. I was expecting a tough match and a close one with not many chances. It was actually quite the opposite, so that was great," he said.

Federer will meet Kei Nishikori after he beat Mikhail Kukushkin 6-3, 3-6, 6-3, 6-4 to make his 12th grand slam quarter-final.

Argentine Guido Pella came from two sets down to beat 2016 finalist Milos Raonic 3-6, 4-6, 6-3, 7-6 (7-3), 8-6 and set up quarter-final with Robert Batista Agut, who beat Benoit Paire, winning 6-3, 7-5, 6-2.

Belgian David Goffin beat Fernando Verdasco 7-6 (9), 2-6, 6-3, 6-4 to set up a meeting with Djokovic in the next round.

Despite her fourth round loss at Wimbledon, Barty's place at the top of the WTA rankings is safe for now as the last woman who could take it from her this week, Czech Karolna Plkov, also failed to reach the quarter finals overnight.

1-Novak Djokovic (SRB) v David Goffin (BEL)

8-Kei Nishikori v 2-Roger Federer (SUI)

Sam Querrey (USA) v 3-Rafael Nadal (ESP)

26-Guido Pella (ARG) v 23-Roberto Bautista-Agut (ESP)

DPA, AAP