Serena Williams laments 'worst two weeks' following exit to teenager Sloane Stephens

Tournament favourite struggled with injury

Serena Williams claimed she was “almost relieved it's over” after an injury-plagued Australian Open campaign ended at the hands of teenage prodigy Sloane Stephens.

Williams suffered a twisted ankle in her opening-round whitewash of Edina Gallovits-Hall and then saw her hopes of advancing to a semi-final meeting with Victoria Azarenka compromised today by a lower back problem sustained in the second set.

At the time, she was in front and looking good to secure a place in the last four in Melbourne for the sixth time but Stephens made the most of her good fortune to go through 3-6 7-5 6-4.

Asked if it was the worst two weeks she had ever had at a grand slam, Williams said: "At a grand slam, absolutely.

"I'm almost relieved it's over because there's only so much I felt I could do.

"It has been difficult. I have been thrown a lot of balls this week."

To focus solely on Williams would be unfair on Stephens, however.

The 19-year-old from Florida showed remarkable poise in her first grand slam quarter-final to come through against her fellow American and childhood hero.

She was competitive in the early going but a solitary break handed Williams the first set.

And when the 15-time major winner broke again to go 2-0 up in the second, few were expecting a comeback from the world number 25.

But she started swinging freely, perhaps realising that she needed to change tack to stand any chance of handing her opponent her first defeat since August.

And it worked. She got it back on serve before the momentum swung even further in her favour at 4-3 when Williams pulled up after charging to the net trying to run down a Stephens mis-hit.

Stephens promptly broke with Williams attempting to limit further damage by gently pushing the ball over the net.

But the teenager, 12 years Williams' junior, got the jitters in trying to serve out the set and the world number three - having left the court for a medical time-out - bravely returned to make it 5-5.

Stephens came again, though, taking the next two games to level the match.

Williams' frustration boiled over after three games of the decider as she was handed a code violation for smashing her racket into the court.

She was, at least, moving better at that stage as the medication prescribed earlier started to kick in.

Williams broke for a 4-3 lead but Stephens was not going away and she hit straight back before edging 5-4 up.

And this time it was Williams who buckled as a series of tired groundstrokes gifted Stephens the win of her life.

Having admitted to some pre-match doubts, Stephens revealed she gave herself a pep talk to restore some belief.

She said: "When I got up this morning I was like, 'look dude, you can do this - go out and play and do your best'."

Current world number one Azarenka earlier beat Svetlana Kuznetsova 7-5 6-1 to keep the defence of her title on track.

Kuznetsova, a two-time former grand slam champion, proved she is over the knee surgery which forced her to miss the second half of 2012 with a wonderfully creative display - mixing clever angles with raw power.

But it was not enough to derail Azarenka, who, having edged the first set, ran through the second to register her 12th successive win in Melbourne.

"She played really well throughout the whole match," Azarenka said. "I know what kind of tennis she is capable of and in the beginning it took a little bit of adjustment because she has a very different game.

"I am glad I could produce my best tennis when it was needed."

Kuznetsova led 4-1 in the first set after displaying a brand of tennis which bamboozled the top seed.

But Azarenka eventually worked it out and powered her way back into the contest.

She broke back for 3-4 and then ramped up her performance level even further at 5-5 with a big forehand on break point edging her ahead for the first time in the match.

She served it out and then maintained the momentum by breaking in the opening game of the second.

Kuznetsova hit back immediately but she could not win another game as Azarenka marched on.

PA