Despite failing 2-1 behind, Au, unseeded, earned her first victory over France's world number five Camille Serme in six years with a scoreline of 5-11, 11-8, 9-11, 11-7, 11-6 at the Bay Club San Francisco.

"I'm feeling really happy, it's been a long time since I beat her," Au said after her World Tour win.

"She's been playing very well over the last few years so I'm very happy with my performance today."

England's fifth seed Perry followed on court for her quarter-final against New Zealand's world number four and second seed, Joelle King, which she won 7-11, 12-10, 11-7, 11-6.

"I've never beaten her before but I tried to put that out of my mind before the match," said Perry.

"I really enjoy playing here in San Francisco.

"I've done amazingly well here and the title last year was the biggest of my career.

"I haven't looked past this match in the draw, it was a huge match against Joelle.

"I'd love to do really well again but it's one match at a time for now."

The evening session heralded the first matches on the Oracle NetSuite SuiteSuccess Court in Embarcadero Plaza where, in a re-match of this year's British Open final, Elshorbagy reaffirmed his status as world number one with a decisive victory over Colombia's world number six Miguel Angel Rodriguez, 11-7, 11-7, 11-8.

"Miguel obviously beat me in the final of British Open and completely deserved it," Elshorbagy said.

"I know just how hard he works and his success as recovering from a drop in form to get back to number six in the world shows his strength of character.

"As much as I was disappointed to lose the British, it was great for the sport to have a South American win the event, but today I was happy that it was me who won our first battle of the season."

Karim Abdel Gawad won an all-Egyptian last eight clash against Tarek Momen, 7-11, 11-6, 11-6, 13-11.

The quarter finals will conclude tomorrow.