Stephens stuns Williams in Melbourne

Sloane Stephens has stunned childhood idol Serena Williams to reach the Australian Open semi-finals.

Williams' chances were seriously hindered by a back injury suffered midway through the second set but credit Stephens, who kept her nerve to complete a 3-6 7-5 6-4 win.

Stephens had a picture of Williams on her bedroom wall growing up and she joked in the post-match interview: "I will have to put up a poster of myself now!"

Third seed Williams looked set to make routine progress through to the last four when she led by a set and a break, but Stephens had other ideas. Starting to display the kind of form which carried her to her maiden grand slam quarter-final, she was hitting freely from the back of the court and made several moves forward to finish points off at the net.

It was turning into a real contest between the experienced Williams and the 19-year-old, understandably tipped as her heiress apparent in American tennis. But then the match took another turn as Williams sustained a back spasm in lunging for a low ball at the net.

The teenager broke for a 5-3 second-set lead and although she could not immediately serve it out - Williams, after taking a medical time-out, bravely hitting back to level it at 5-5 - Stephens regrouped following a bout of jitters to break again and take it to a decider.

Williams' frustration boiled over after three games of the final set, earning herself a code violation for whacking her racket into the court. But she could console herself with the fact her back appeared to be loosening up, perhaps as a result of the medication prescribed earlier starting 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.

She will now meet world number one Victoria Azarenka, who earlier beat Svetlana Kuznetsova 7-5 6-1.

"It should be fun," said Stephens. "I am in the semis of a grand slam so I will give it my all and do the same thing again."