Teenager Stephens rallies to stun ailing Serena

By Greg Stutchbury

MELBOURNE (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 world number one Victoria Azarenka, the 19-year-old maintaining her focus to see out the victory after the five-time champion had jarred her back in the second set and left the court for medical treatment.

"Oh my goodness," an emotional Stephens said in a courtside interview as she secured a maiden grand slam semi-final berth. "I'm sure my grandparents are freaking out. I'm sure they're watching on the computer."

The match was billed as a showdown pitting the future of American tennis against the most accomplished player of the present generation, and the early signs indicated that Williams possessed too much power for her younger opponent.

Both players hammered away at each other on serve in the opener with the receiver winning a total of two points until the eighth game, when Williams broke Stephens to take a 5-3 lead then held to seal the set in 28 minutes.

The nature of the contest changed dramatically when Williams, already concerned by an ankle injury sustained in the first round, appeared to twinge her back when chasing a drop shot in the eighth game of the second set.

Visibly in pain, the 31-year-old's vigor disappeared and she took a medical timeout to have the injury assessed. Tournament officials told ESPN that she was suffering from spasms.

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