American teenager Sloane Stephens produced the biggest upset of the 2013 Australian Open, knocking fellow American Serena Williams out of the tournament with a 3-6, 7-5, 6-4 win in the quarterfinals on Wednesday.

"Today, I just really didn't have anything to lose. I mean, you're playing for the semis of a Grand Slam. You just got to go out and do it really," the 19-year-old Stephens said after the match.

The 31-year-old Williams, who was the No. 3 seed, had not lost a set in the tournament and coasted to a 6-3 win in the first set.

"This morning when I got up, I was like, look, dude, like, you can do this. Like, go out and play and do your best," Stephens said in response to a question about whether she believed she could win the match.

Williams, for her part, lost control in the third set and ended up smashing her racquet.

"I'm almost relieved that it's over," Williams said after the match, referring to her experience at the Australian Open.

Williams and her sister, Venus, were eliminated from the doubles competition on Tuesday by the Italian duo of Sara Errani and Roberta Vinci.

Stephens will face Victoria Azarenka of Belarus in the semifinals.

Azarenka, the defending champion and No. 1 seed, beat Russia's Svetlana Kuznetsova 7-5, 6-1. EFE