Worst Slam EVER: Serena Williams so glad her Australian Open is finally over

Serena Williams claimed she had suffered her worst ever Grand Slam after her shock defeat in the Australian Open to teenager Sloane Stephens.

The hot favourite for the title was hindered by a back injury as the Wimbledon and US Open champion lost for the first time since August. It was also the 31-year-old first defeat to an American younger than her.

The No.29 seed, who beat Laura Robson in the third round, won 3-6 7-5 6-4 in the biggest upset of the tournament.

The winner of 15 Grand Slams had been on a winning run of 20 matches while Stephens was appearing in her first Grand Slam quarter final. But Williams rolled her ankle in the first round here, hit herself in the face with her racquet in the second round, and felt her back seize up.

After smashing her racquet in frustration during the third set against Stephens, courtside microphones heard her complaining this was her worst two weeks at a Grand Slam.

“For a Grand Slam, absolutely,” she said. “Absolutely. Oh, my gosh, I’m almost relieved that it’s over because there’s only so much I felt I could do.  I was unaware the microphones picked that up.

“It’s been a little difficult. I’ve been thrown a lot of balls these two weeks.

“I’ve had a tough two weeks between the ankle, which is like this big every day, and my back, which started hurting.  A lot of stuff.”

Williams had sent down serves of 207kmh earlier in the tournament (128mph) but her back problem saw her only serving at 130khm against the 19-year-old this morning.

“A few days ago it just got really tight and I had no rotation on it.  I went for this dropshot in the second set and it just locked up on me, As I went to hit it, it was on the backhand.  I even screamed on the court.  It was a little painful.

“But it’s okay. It was what it was.  I think everyone at this stage in the locker room has something wrong with them, so it’s fine. There’s no excuse there.”

In her courtside interview, an emotional Stephens said: “Oh my goodness. I’m sure my grandparents are freaking out. I’m sure they’re watching on the computer.”

She will now face Victoria Azarenka after the world No.1 won her 12th consecutive match at Australian Open.

The defending champion beat Svetlana Kuznetsova 7-5 6-1 despite trailing 4-1 in the first set.

Maria Sharapova meets Li Na in the other semi in the early hours of Thursday UK time.

Serena Williams will still finish the tournament as world No 1 if Sharapova loses in the semi and Azarenka fails to retain the title.