Citing health setbacks as the main reason, former No. 1 player Ana Ivanovic, 29, announced her retirement from tennis on Wednesday.
In what was tabbed as a blockbuster potential matchup when the draw was released, Serena Williams will meet Maria Sharapova in the quarters after both won in straight sets Sunday.
Maria Sharapova overcomes a lack of playing time to easily win her first-round match at the Australian Open.
Serena Williams said Thursday she is withdrawing from the season-ending WTA Finals and the China Open to take time to heal after playing through injuries all year.
On the eve of the event, Maria Sharapova announced via Facebook that she will not play in the US Open. Sharapova has been out of action since a semifinal loss to Serena Williams at Wimbledon.
Garbine Muguruza is confident she can beat Serena Williams in the Wimbledon final on Saturday, saying "she knows that I can win against her, that I'm not afraid."
