Venus Williams, the former world's number one and currently ranked 44, defeated here Wednesday Serbia's Ana Ivanovic 6-2, 6-1.
Her younger sister Serena Williams, the current number one, kicked out Elaterina Makarova the evening before 7-6, 6-0.
Ivanonic appeared to be exhausted during the game as the 26-year old Serbian had a tough Tuesday behind her when she beat Germany's Angelique Kerber in three tough sets, reported Xinhua.
For Williams, the victory was a revenge for her defeat in the final in Auckland, New Zealand, earlier this year.
Thirty-three-year-old Venus Williams will face Flavia Panetta from Italy in the quarter finals.