As of now the only U.S. female that remains in the tournament Down Under is 19-year-old Sloane Stephens after a 3-6, 7-5, 6-4 upset victory on Wednesday during the quarterfinals of the Australian Open.

Williams, who won the first set at 3-6, dropped the second and third at 7-5 and 6-4 after suffering a lower back injury as she was trying to avoid the net.

Stephens kept her composure, blocking out the injury issue on the opposite side of the net, and rallied for a 3-6, 7-5, 6-4 victory on Wednesday -- by far the most significant in her seven Grand Slams.

"This was so crazy," said Stephens, who hangs a poster of Serena. "I think I'll put a poster of myself up now."

Regarding the match, Stephens reflected.

"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."

Stephens career started in high school when she managed to finish the U.S. Open Junior doubles as a runner-up alongside teammate Mallory Burdette in 2008. Later that same year she made it into the Grade A Orange Bowl semifinals as a wildcard.

Her victory over Williams earned her world number 25 rank in the pro league. She is now the youngest woman currently ranked in the WTA top 40.

After the biggest victory of her career, Stephens now moves on to the semifinals to face world number one Victoria Azarenka after taking out Swetlana Kuznetsova in her quarterfinal match.

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