The Australian Open was left without a defending champion in the semi-finals for the first time in the professional era when Victoria Azarenka followed Novak Djokovic out of the door today.

Azarenka, champion for the last two years, tumbled out with a 6-1 5-7 6-0 loss to Agnieszka Radwanska less than 15 hours after Djokovic, who had been in the hunt for a fourth straight title, was upset by Stanislas Wawrinka in his quarter-final.

Radwanska went for broke to snap the Belarussian's 18-match winning streak at Melbourne Park with a thoroughly deserved two-hour victory on Rod Laver Arena and set up a semi-final meeting with Slovakia's Dominika Cibulkova.

Cibulkova shocked Maria Sharapova in the fourth round and kept up her momentum in fine style by dismantling Simona Halep 6-3 6-0 to move into a last four missing the top three seeds after Serena Williams was dumped out in the last 16.

China's fourth seed Li Na, now a strong favourite to win her first Australian Open crown, will meet Canadian teenager Genie Bouchard in the other women's semi-final tomorrow.

Azarenka came into Wednesday’s match as the only woman not to have given up a set in the tournament but Radwanska, who had lost 12 of their 15 previous meetings, wasted no time in giving her a reminder of how it felt.

The Pole raced out to a 5-0 lead and although a furious Azarenka finally managed to hold serve at the third attempt, Radwanska took a 1-0 lead after 33 minutes.

Azarenka did not win two Australian Open titles without knowing how to scrap a bit when necessary, though, and charged back to win a tight second set in just under an hour with a fierce forehand winner.

The shriek with which she celebrated levelling up the match failed to galvanise her, though, and Radwanska, scuttling around the court to retrieve everything the Belarusian could throw at her, whipped through the decider in another half an hour.

“I think it’s hard to play someone I lost to so many times before. I knew she was great player. Especially here, she’s playing amazing tennis,” said fifth seed Radwanska, losing finallist at Wimbledon in 2012.

“But I really had nothing to lose. She was defending the title, not me. I was really trying to play my best tennis, go for every shot I could. I’m just very happy because I really was playing great tennis.”

Azarenka, who hit 47 unforced errors, clearly laid the blame for her defeat at her own door but leavened her self-flagellation with some praise for her opponent.

“She was aggressive. She was making everything. She was guessing right. I was just playing a little bit too predictably,” said the 24-year-old.

“It’s not the end of the world. I’m not happy with what I did today (but) I can’t take away what she’s done. She played amazing. She really was on top in the longer rallies and way more accurate than me.”

An aggressive gameplan also paid dividends for 20th seed Cibulkova as she demolished a hapless Halep in the opening match on Rod Laver Arena.

The Slovakian dominated from the baseline, keeping her opponent pinned down with her deceptively strong groundstrokes to reach her maiden grand slam semi-final.

The Romanian, who won six titles in her breakthrough season last year, admitted she had simply been unable to cope with the pressure of her first grand slam quarter-final.

“I just couldn’t play today,” said Halep. “I had emotions, big emotions, and I couldn’t manage this. Before the match I was very nervous and I didn’t feel the ball at all. I couldn’t move my body and I couldn’t play.”