WIMBLEDON 2010, England -- Defending champion Serena Williams overcame Maria Sharapova 7-6 (9), 6-4 on Monday to reach the Wimbledon quarterfinals and avenge her loss to the Russian in the 2004 final. Serena Williams served 19 aces for the second straight match -- taking her total to 63 for the tournament -- and held off the resurgent Sharapova in a tight battle on Centre Court Venus Williams overcame a tough challenge from the lowest-ranked player left in the draw. The second-seeded Williams broke back twice to stay in the second set, then escaped in the tiebreaker to complete a 6-4, 7-6 (5) victory on Court 2 over 92nd-ranked Jarmila Groth of Australia. The victory sent Williams into her 31st Grand Slam quarterfinal and improved her record to 12-0 in fourth-round matches at the All England Club. She could potentially face Serena in Saturday's final.