Defending champion Agnieszka Radwanska of Poland has been defeated 7-5, 6-3 by American qualifier Bethanie Mattek-Sands at the Sydney International on Tuesday.
Mattek-Sands, who is back on tour after a long layoff with a knee injury, lost in the first round in Brisbane last week and had to win three matches just to qualify for the main draw in Sydney, and advances to play the winner of the match between fellow American Madison Keys and Croatian wild-card entry Ajla Tomljanovic.
According to Sport24, Angelique Kerber of Germany was also through to the quarterfinals after beating Kaia Kanepi of Estonia 6-3 6-4.
Both the Brisbane and the Sydney Internationals are tuneup events for the Australian Open, which begins next week, the report added.