Melbourne, Jan 23 (IANS): Defending champion Victoria Azarenka overcame early jitters to beat Svetlana Kuznetsova here on Wednesday and advance to the Australian Open semifinals while one of her rivals and tournament favourite Serena Williams suffered a shock defeat to American teenager Sloane Stephens.

After dropping serve in a long fourth game which went to deuce 10 times, Azarenka recovered to dominate the rest of match and canter to a 7-5, 6-1 win, reports Xinhua.

Azarenka broke Kuznetsova's serve in the 11th game of the one hour 17 minutes match and then held her own service in the next game to win her third set point when Kuznetsova netted a backhand.

"I'm just glad I could produce my good tennis when it was needed." said Azarenka.

Azarenka will meet 19-year-old Sloane Stephens, who stunned Serena 3-6, 7-5, 6-4.

Williams, who was troubled by ankle problems earlier in the tournament, required treatment for back spasms and smashed her racquet as the match slipped away.

"This is so crazy," said Stephens, who used to have Williams' poster on her bedroom wall. "I think I'll put a poster of myself up now.