Elsewhere, Belgium's Elise Mertens upset second seed Sofia Kenin of the United States 6-3, 6-3 to also make the last eight.
Playing in his second match for the Rio de Janeiro outfit, the 35-year-old combined with Rhuan Silveira before deftly sliding a shot past Cassio.
"Serena is Serena," Sakkari said after advancing earlier on Saturday by beating 19-year-old American Amanda Anisimova 6-3, 6-1. "You have to come up with some great tennis. Otherwise there is no chance against her." Enditem
World champion Daniel Stahl took his 13th consecutive victory in the men's discus, with the Swede throwing 67.28m.
Sakkari threatened to repeat her come-from-behind victory over Williams in the Western & Southern Open two weeks ago, but ultimately fell just short.
"We are calling the CFA to further regulate the behavior of the agents and effectively protect the legitimate rights and interests of youth training institutions and young players," the letter said. Enditem
In the men's shot put, Ryan Crouser of the U.S. won with a throw of 22.70m, followed by Poland's Michal Haratyk and Leonardo Fabbri from Italy.
Hazard could be Madrid's 'signing' of the summer. The winger arrived unfit 12 months ago and struggled with injuries all season, but anyone who has seen him play for Chelsea knows what Hazard can do, and if the Belgian returns to his best he will add another dimension to Madrid's front line in terms of movement, dribbles, assists and goals.
The midfielder then posted a message to fans on social media as he prepared to undergo surgery to repair his ACL.
"It was a pity that we lost in stoppage time last game. We followed coach Van Bronckhorst's plan and all players focused on the game tonight, I'm glad to see that, and we deserved the win," said Saba.
CHENGDU, Sept. 8 (Xinhua) -- Powerhouse Qingdao Renzhou suffered its first season loss in the 11th round of the China Badminton Super League (CBSL), after going down to Ruichang Biyuan 3-2 here on Tuesday.