Serena Williams really hates this racket. (Matthew Mallett / Getty Images)

Serena Williams was rolling, looking as if she might be as dominant as she has ever been as she made her way through the Australian Open.

And then, just like that, it all fell apart. Williams, the tournament’s No. 3 seed, was headed home and 19-year-old American Sloane Stephens was a 3-6, 7-5, 6-4 winner in a shocker Down Under.

Williams, coming into the tournament off wins at Wimbledon and the U.S. Open and an Olympic gold medal in London, was up a set and a break when pulled up on a drop shot and hurt her back. She took an injury timeout, her second of the tournament, and went on to lose her first set since the U.S. Open. Her game continued to disintegrate, as did her racket, which she smashed against the court in frustration.

Stephens’s first move after winning was, of course, to check her cellphone (which had 145 messages waiting). Rather than Williams, who had won 20 straight matches, the semifinal will now feature Stephens against Victoria Azarenka, the No. 1 player in the world. Beating Williams was mind-blowing for Stephens, who said that a poster of Williams hung on her wall.

“This is so crazy, but oh, my goodness,” Stephens said as she wiped away tears in her post-match interview. “I think I’ll put [up] a poster of myself now.”

Williams, 31, lost in the first round of the French Open last year, but this was her first loss to a younger American woman.

Sloane Stephens moves on to the semis. (Mark Baker / AP) Sloane Stephens moves on to the semis. (Mark Baker / AP)

“Last night I was thinking about it,” Stephens said. “And someone asked me, ‘Do you think you can win?’ And I was like, ‘Yeah, I think so.’ But I wasn’t too clear about it, and this morning when I got up I was like, ‘Dude, you can do this. Go out and play and do your best.'”

After she tweaked her back, Williams was never quite the same, losing some speed on her serve.  “A few days ago [my back] got really tight and I had no rotation on it,” Williams said. “I went for this drop shot in the second set and it locked up on it, and I couldn’t really rotate after that.”

With Stephens leading 2-1 in the third set, Williams failed to break serve and took two mighty swings at the court with her racket. It crumpled and she threw it at her bench, drawing a code violation for equipment abuse.

Williams, who lost 16 games to Stephens after dropping only eight in the tournament, had rolled her ankle in a match last week, requiring her first injury timeout of the tournament. “I’ve had a tough two weeks between the ankle, which is like this big every day,” she said, holding her hands far apart, “and my back, which started hurting. A lot of stuff.”

Not that she was thinking about retirement. “Are you kidding me? I don’t think about retiring,” Williams said in response to a reporter’s question, then realized he wasn’t talking about anything permanent and laughed. “Oh, you mean about the match. I thought you meant my career. I though about it for like a nanosecond.”

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