Charleston (South Carolina): Serena Williams reached the Charleston WTA clay court semifinals on Friday when injury-cursed Sabine Lisicki quit their last-eight clash in floods of tears.

The American fifth seed was 5-1 ahead in the first set when her German opponent, whose career went into a tailspin in 2010 when an injury left her barely able to walk, retired having fallen and injured her ankle.

Williams, who could face sister Venus in the semifinals, won warm applause from the crowd as she tried to console the stricken Lisicki.

"I totally get it," said Williams, who has endured her own battles with injury and illness, when asked if she sympathised with the German.

Earlier Friday, Australian second seed Samantha Stosur reached the quarterfinals after seeing off Galina Voskoboeva of Kazakhstan 6-3, 4-6, 6-2 in a third-round match held over from Thursday because of rain.

Stosur will face Venus Williams for a place in the last four.

The other quarterfinals feature Slovenia's Polona Hercog against experienced Russian Nadia Petrova and Vera Zvonareva of Russia playing Lucie Safarova of the Czech Republic.