Osaka, Tsitsipas through to China Open quarterfinals

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 here on Thursday.

Action on the Diamond Court got underway with 16th seeded Caroline Wozniacki overcoming several scares to edge past Czech No. 47 Katerina Siniakova in straight sets 7-5, 6-4.

The two traded breaks twice in the first set to go 4-4, with both players keeping it tight and committing very few unforced errors. Siniakova would be the one to blink first when serving to force a tiebreak at 5-6 with several netted errors.

Wozniacki went a break up to go 4-1 in the second, only to watch that lead shrink to 5-4 off a double fault and then a series of netted unforced errors when serving for the match.

Undeterred, Wozniacki turned it around to respond with a break of her own and seal the win in just over 90 minutes.

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.

Osaka was slow getting into form, while Riske was very agile out of the gate, fighting her to deuce on her opponent's first two service games before finally converting to go a break up at 4-2.

But Osaka quickly turned things around in a big way. After being held to 30 in the sixth game of the first set, she went on to win every remaining game of the match.

"I think getting into the rhythm [was crucial in the first set]. It seemed like she was the type that would use my pace [to her advantage], especially on the forehand. I just tried not to give her too much," Osaka said after the match.

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.

Already on a 15-match winning streak, Andreescu continued her good form in the first set, breaking Brady three times on the way to sealing things up with ease.

Although Brady held serve to 3-3 in the second set, Andreescu kept finding the depth of the court and closed out the match in a little over one hour.

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.

The two players each held their service games out to 6-6 in the opener, with both Isner and Evans holding to love at least once on the way to the tiebreak, when the American would take the first breaks of the match to grab the opener.

Neither side gave much in the second set either, holding to 5-5 before Isner got a crucial break to go one up and avoid another tiebreak.

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

The first set saw Basilashvili nab an early break to go 2-1 up, a lead that he would maintain for the rest of the opener as the two served out the remainder.

The second set was something of an inversion of the first. Basilashvili started coughing up unforced errors on both sides, allowing Tsitsipas to drag him to break point three times before converting to go 3-1 up.

Five double faults from the Georgian would help Tsitsipas run away with the second set and force a decider, where he would go on to break Basilashvili twice more while never facing a break point himself to seal the win in two hours and ten minutes.

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 comprehensively outplayed his younger rival, holding all his service games and dominating the match both from the baseline and at the net, and the gulf in class between the two was all too evident as Zverev closed out the match in just over one hour.

The German's reward for his victory is a quarterfinal tie against 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

Quarterfinal action in Beijing will take place on October 4.