Alexander Zverev beat racket snapper Corentin Moutet on Sunday to book a quarter-final date with Daniil Medvedev at the China Open as Coco Gauff kept her title defence hopes alive.

The world number three from Germany kept his calm to edge out the Frenchman 7-5, 3-6, 6-3 and set up a 21st Tour meeting with his Russian rival.

"I'm looking forward to the quarter-finals and playing my good friend Daniil," Zverev said after the match.

Zverev held on in the first set to get the better of an angry Moutet, whose racket met its end against the 26-year-old's leg.

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Corentin Moutet broke his racket against his leg / © AFP

The world number 37 won set two, producing several drop shots to keep Zverev on the run, but it was the German who cleaned up shop in the decider.

"(Moutet is) a good player, so difficult match. He's beaten a lot of great opponents this year," Zverev later told AFP.

"I'm gonna do everything I can," the 28-year-old said of his upcoming Medvedev meeting. "If it's enough in the end, then great, and if it's not, then it's also OK. I'm looking forward to a tough battle."

Earlier on Sunday 29-year-old Medvedev put away Spaniard Alejandro Davidovich Fokina 6-3, 6-3 in an hour-and-a-half without much fuss.

And Lorenzo Musetti apologised on court for an outburst at coughing fans earlier in the tournament.

Fans booed when the 23-year-old Italian entered the court for his match and some were making loud guttural coughing noises.

"I totally understand your point and I... regret what I've said and what I've done, so sorry, thanks for understanding," he said in English after beating France's Adrian Mannarino 6-3, 6-3 to move into the quarter-finals.

The on-court interviewer, however, did not translate his apology into Chinese for the fans, only relaying Musetti's brief comments about the match.

- Gauff marches on -

In the women's draw, defending champion Gauff fought through a tough examination by Leylah Fernandez, battling through 6-4, 4-6, 7-5 to keep her hopes of winning back-to-back China Opens alive.

"I did what I needed to do to win today," the 21-year-old American said.

"It was very physical," Gauff said. "We were going back and forth."

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Coco Gauff serves against Leylah Fernandez in Beijing / © AFP

Gauff looked in control in the first set but the gritty Fernandez hit back in the second to force a decider.

The 25th-ranked Canadian survived a match point to level at 5-5 but Gauff finally clinched the 2hr 45min marathon when Fernandez netted.

The world number three next plays Switzerland's Belinda Bencic for a place in the quarter-finals.

Also in the women's event, US Open finalist Amanda Anisimova spoiled the party for home player Zhang Shuai, getting through 7-6 (13/11), 6-0 just before midnight.

Germany's Eva Lys stunned world number 10 and former Wimbledon champion Elena Rybakina 6-3, 1-6, 6-4.

"I was trying to get a top-10 win the whole year," said the 23-year-old Lys, ranked 66.

"This is my first one. I'm very happy I finally got it done."

Poland's Iga Swiatek is the top seed at the WTA 1000 event after world number one Aryna Sabalenka withdrew.

Italy's Jannik Sinner is the top seed in the men's ATP 500 event being played alongside the women's tournament.