Stephens' victory over Serena Williams yesterday seemed to take its toll on the 19-year-old in the early stages but she grew into the contest and was starting to get on top before Azarenka limped over the line, aided by a medical time out at a vital juncture.

The Belarussian will meet Li Na in Saturday's final knowing she also needs to beat the Chinese to retain the number one ranking from Williams.

But she has plenty to think about beforehand.

Not only did Azarenka buckle when almost in the winner's circle she also cut a tetchy figure, frequently smashing balls all over the court in frustration at her inability to put the teenager away.

"I almost did the choke of the year," she admitted. "At 5-3 and having so many chances I couldn't close it out.

"I felt a little bit overwhelmed and realising I was one step away, nerves got into me.

"Until 5-3 I was very happy with my performance and after that it wasn't my best but it's important to overcome this struggle and finish the match."

Stephens, in her first grand slam semi-final, looked understandably nervous early on and Azarenka seized on her uncertainty by running through the opening two games.

The 29th seed finally got on the board thanks to a brilliant backhand winner in game three but she remained edgy and Azarenka broke for a second time to establish a 4-1 lead.

Azarenka dropped just three points on serve in the opening set and she clinched it with a third break drawing her opponent into the net before delivering a brilliant top-spin lob over her head for a winner.

And when she swiftly moved 2-0 ahead in the second it looked plain sailing for the top seed.

But then came the injury scare as she pulled up after chasing down a wide backhand with her left ankle the area of concern.

Stephens, who profited when Williams hurt her back in their last-eight clash yesterday, sensed the door may be opening once more.

She broke back and then held to get it back to 2-2.

Azarenka promptly embarked on a run of nine successive points which moved her to 4-2 only to toss her away her advantage when two double faults and a mis-timed backhand gifted Stephens a break back.

Azarenka's frustration was evident but, rather than pin her down, the inexperienced Stephens let her off the hook, playing an error-ridden game in which the world number one did little to earn her break.

Serving at 5-3, the 2012 champion wobbled horribly and saw five match points come and go as Stephens fought bravely although she was helped by Azarenka's fragile mental state.

Then came the controversy as Azarenka took a near 10-minute medical time-out for an unspecified injury seemingly unrelated to her ankle.

When she returned she regained her composure and broke at the first opportunity to set up a clash with Li.

Li crushed Maria Sharapova with a magnificent display to power into her second Melbourne final.

Sharapova had broken a tournament record in conceding just nine games in reaching the last four but she was overwhelmed by the Chinese whose heavy-hitting, high-risk game reaped maximum reward.

In the face of blazing winners from all angles, Sharapova, the second seed, had no answer as Li romped to a 6-2 6-2 win.

"I always play well here," observed Li after a 93-minute masterclass.

Li, who reached the Melbourne final in 2011 and a few months later become the first Asian player to win a grand slam crown at Roland Garros, set the tone early on, two breaks of serve handing her a 4-1 lead her dominance merited.

Sharapova got one back but the world number six swiftly reasserted her authority by breaking again before wrapping up the first set.

A shellshocked Sharapova battled to find a route back into the contest in the second but could not find any fluency as her opponent's greater power and clever angles consistently put her on the back foot.

The Russian saw a break point swatted aside with another forehand winner from Li and she could not get any closer due to an uncharacteristically high 32 unforced errors.

Li broke for 3-2 and then again for 5-2 thanks to a backhand winner.

Not for the first time, Li got the jitters in attempting to close out the match but another sloppy groundstroke from Sharapova did the job.