Terra

Foto: Toby Melville / Reuters

American teenager Sloane Stephens caused the biggest upset at this year's Australian Open when the 29th seed rallied to overcome an injury-hampered Serena Williams in the quarter-finals on Wednesday.

Stephens prevailed 3-6 7-5 6-4 to set up a semi-final against defending champion Victoria Azarenka, the 19-year-old maintaining her focus to see out the victory after the five-time champion jarred her back in the second set and left the court for medical treatment.

Williams, the pre-tournament favorite, had smashed a racquet in frustration early in the deciding set and while her anger appeared to motivate the 31-year-old enough to break Stephens' serve, her opponent showed plenty of maturity and broke straight back.

Stephens then held and broke Williams in the final game to set up a last four encounter against the world number one.

The American teenager has not won a tournament as a professional and still has a tough road to go before lifting the Australian Open trophy as to do so she will likely have to defeat the top three seeds, including Williams and Azarenka with a possible matchup against Maria Sharapova -- who plays  Li Na in the other semi-final -- looming in the finals.

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