American teenager Sloane Stephens has pulled off one of the major upsets in Australian Open history.
The 19-year-old defeated five-times champion Serena Williams on Wednesday to reach the semi-finals and a date with world No.1 Victoria Azarenka.
Stephens, seeded 29th, won 3-6 7-5 6-4 in 2 hours 17 minutes.
Earlier, defending champion and top seed Victoria Azarenka beat Svetlana Kuznetsova of Russia 7-5 6-1.