The German, who has battled back from a career-threatening ankle injured, appeared to hurt the ankle again as she departed in tears having been 5-1 down at the time.

Williams, who will face reigning US Open champion Sam Stosur in the last four, won warm applause from the crowd as she tried to console the stricken Lisicki.

Stosur booked a last four date with Williams after overcoming Galina Voskoboeva and Venus Williams in the same day.

First the Australian completed a 6-3 4-6 6-2 win over Voskoboeva in their rain-interrupted third-round match before denying an all-Williams semi with a battling 6-3 4-6 6-3 victory over Venus.

The other semi-final will be contested between Lucie Safarova and Polona Hercog.

The ninth-seeded Czech Safarova stunned No.4 seed Vera Zvonareva 6-3 6-3, while Hercog of Slovenia breezed past 13th-ranked Russian Nadia Petrova 6-1 6-2.