HONG KONG -  Defending champion Caroline Wozniacki and world number four Elina Svitolina both withdrew from the Hong Kong Open with injuries Thursday, leaving the WTA event devastated after a spate of pre-tournament pullouts and early big name exits.

A tearful third seed Wozniacki appeared on centre court just after her second-round match against Lizette Cabrera had been due to start to announce she had injured her elbow in practice. "I want to apologise to everyone who came out today to watch this match," said an emotional Wozniacki, who won the title on the same court 12 months ago.

"I did everything I could possibly to get ready for today," she told the crowd. "But unfortunately I hurt my elbow during practice and there's just no way I could perform my best out here today. "Unfortunately I have to withdraw from the tournament," she added choking back tears. Top seed Svitolina earlier withdrew from her last-16 match against Nicole Gibbs citing a right groin strain sustained during a mammoth, 3hr 21min quarter-final defeat in Beijing last week to the eventual champion there, Caroline Garcia. "I picked up the injury a little bit in Beijing," she said. "It's the groin. All the time when I go for wide shots or stretch I feel it.

Ukraine's Svitolina and Denmark's Wozniacki both have one eye on this month's lucrative WTA Finals in Singapore where the top eight will battle it out for a massive $7 million prize fund. "I will probably do some scans now to see how it is, because you know I have Singapore," admitted Svitolina. "It's a tough decision because I really wanted to play here." The tournament, which has just two seeds left standing at the last-eight stage, was rocked even before it started by the pullouts of three other big names. US Open champion Sloane Stephens cried off with an injury after losing in the first round in both Wuhan and Beijing, her only appearances since her Flushing Meadows triumph.

British world number 10 Johanna Konta also cancelled her trip because of a foot problem, while France's 13th-ranked Kristina Mladenovic opted out with a knee injury. Of the star players that did show up at Victoria Park, number two seed Venus Williams was sent packing in her second-round match in straight sets on Wednesday by Japanese teen sensation Naomi Osaka.

And she was swiftly followed by fourth seed Agnieszka Radwanska of Poland, beaten in three sets by the resurgent former US Open champion Sam Stosur. In the little action that did take place on court Thursday, China's eighth seed Zhang Shuai was ousted by American Jennifer Brady 6-3, 6-4 who will face Gibbs in an all-American quarter-final.

It left Wang Qiang as the sole Chinese representative in the draw after she breezed past Thailand's Luksika Kumkhum 6-4, 6-4. Wang will face Australia's Stosur in Friday for a place in the semi-finals and Cabrera, the world number 155, has an all-Australian last-eight match against Daria Gavrilova, the seventh seed.

The only other seed remaining, number six Anastasia Pavlyuchenkova, will play Osaka.

Big-hitting American Brady, ranked 70, easily overcame an out-of-sorts local crowd favourite Zhang 6-3, 6-4 in just over an hour. Brady smacked down seven aces to overpower the world number 31, whose inconsistent serve was broken three times in the second set alone. "I started strongly with the first break and was aggressive," said Brady. "So I'm happy with the win."