Beijing, Oct 4 (IANS): Round of 16 action at the 2019 China Open ended with the defending men's singles champion crashing out, while other top seeds moved into the quarterfinals.

On Thursday, 16th seeded Caroline Wozniacki overcame several scares to edge past Czech No. 47 Katerina Siniakova in straight sets 7-5, 6-4, reports Xinhua news agency.

Up next for Wozniacki is Daria Kasatkina, after the Russian defeated her compatriot Ekaterina Alexandrova 6-4, 6-3, despite making no fewer than nine double faults over the course of the match.

World No. 4 Naomi Osaka of Japan logged another straight-set win, moving past Wuhan Open runner-up Alison Riske 6-4, 6-0.

The Japanese now faces a quarterfinal against US Open champion Bianca Andreescu, after the Canadian made short work of qualifier Jennifer Brady, defeating the American 6-1, 6-3.

In the men's draw, world number 19 John Isner fired off 21 on his way to a hard-fought 7-6 (3), 7-5 win over British qualifier Daniel Evans in just under two hours.

Isner faces 3rd seed Stefanos Tsitsipas in the quarterfinals, who stunned defending China Open singles champion Nikoloz Basilashvili 4-6, 6-3, 6-2 in a three-set marathon.

The last men's match of the day saw No. 2 seed Alexander Zverev issue a real statement of intent, dispatching Felix Auger-Aliassime of Canada 6-3, 6-1 in impressively quick fashion.

The German will face Sam Querrey, after the American served up 32 aces on his way to defeating Argentina's Diego Schwartzman 7-6 (2), 6-7 (6), 6-3.