Serena knocked out in quarters

MELBOURNE, Australia — Serena Williams is out of the Australian Open after losing her quarterfinal match 3-6, 7-5, 6-4 to 19-year-old American Sloane Stephens.

Williams appeared to hurt her lower back while attempting to pull up short of the net during the eighth game of the second set. She called for a trainer after the ninth game with the score 5-4 and on serve.

Stephens won the second set when Williams, serving slower than usual, was broken. Williams also had her service broken in the final game of the match.

At 2-1 and on the way to a changeover in the third set, Williams smashed her racket angrily on the court then threw it toward her chair.

Stephens will play defending champion Victoria Azarenka in the semifinals.

With her most famous fan sitting in the crowd wearing a shirt reminding her to keep calm, defending champion Azarenka overcame some early jitters to beat Svetlana Kuznetsova 7-5, 6-1.

After dropping serve in a long fourth game which went to deuce 10 times, Azarenka recovered to dominate the rest of the match against Kuznetsova, a two-time major winner who was floating dangerously in the draw with a No. 75 ranking as she recovers from a knee injury.

Azarenka's American rapper friend, Redfoo, returned from a concert in Malaysia to attend Wednesday's quarterfinal match.

Wearing a red sleeveless T-shirt that read Keep Calm and Bring Out the Bottles, the name of his next single, Redfoo stood, clapped and yelled Come on, Vika! during the tight first set.

Asked if it helped to have her No. 1 fan wearing a keep calm logo, Azareka said I was looking more at the part that says ‘Bring out the bottles.'

Of her game, she added, I'm just glad I could produce my good tennis when it was needed.

In the men's quarterfinals, 17-time major winner Roger Federer was playing No. 7 Jo-Wilfried Tsonga in a night match and U.S. Open champion Andy Murray was to meet Jeremy Chardy of France.

Novak Djokovic is already through the semifinals after his 6-1, 4-6, 6-1, 6-4 win over fifth-seeded Tomas Berdych on Tuesday night.

The 2-hour, 31-minute victory took exactly half the time of his five-set, fourth-round win two nights previously against Stanislas Wawrinka.

It was a great performance. I was hoping to have a shorter match ... just not to go over 5 hours, Djokovic said, in a comparatively subdued mood Tuesday after a considerably more routine victory. It's always going to be tough against Tomas; he's an established player. He has a big game, big serve. He can compete against anyone on any surface.

In the semifinals, Djokovic will meet No. 4-seeded David Ferrer.

Ferrer survived a quarterfinal battle with fellow Spaniard Nicolas Almagro. Almagro had three chances to serve for the match, but Ferrer broke back each time and went on to win 4-6, 4-6, 7-5, 7-6 (4), 6-2.

Maria Sharapova had a 6-2, 6-2 quarterfinal win over Ekatrina Makarova earlier Tuesday, and has conceded only nine games in five matches — a record in Australia.