Melbourne: Sloane Stephens, seeded 29th, pulled off the biggest surprise of the Australian Open so far beating Serena Williams in the quarterfinals here Wednesday.
Stephens, 19, gained revenge on Williams for her defeat in Brisbane three weeks earlier with a 3-6, 7-5, 6-4 win.
"Yeah, I don't know how I feel. It's still strange," Stephens was quoted as saying on the tournament website.
"This morning when I got up, I was like, look dude you can do this. Like, go out and play and do your best."
Five-time Australian Open champion Williams was 4-5 down in the second set when she sprained her back and went to the locker room to receive treatment.
After she returned, Stephens closed out the set but still faced a tough task to beat the hampered Williams, who later blamed her poor recent injury record for the defeat.
"I've had a tough two weeks between the ankle which is like this big every day, and my back, which started hurting," Williams said.
In the semifinal, Stephens will face reigning champion Victoria Azarenka, who defeated Russia's Svetlana Kuznetsova 7-5, 6-1.
"I think we were both producing, you know, good tennis, but I felt like she was a little bit on top of me on the important moments. Then I turned it around and I took control in my hands and it was more up to me," Azarenka said praising her next opponent.
"I think Sloane is a very, very talented girl. I think over the last couple years you see her development, you know, as a tennis player."
Azarenka surged back from 1-4 down in the first set. Kuznetsova's attempt at a second set fightback was hampered in the first game of the second set when she injured her knee, which caused her to miss most of last season.
"I was really scared because I almost broke it again the same way I did it," Kuznetsova said.
"I was a little bit freaking out because I didn't want to have another time off."
The second semifinal will pit second seed Maria Sharapova of Russia against Chinese sixth seed Li Na.