Melbourne: The determined Pole battled to a 6-1, 5-7, 6-0 win to send the Belarusian packing with the top three seeds now out of the Grand Slam following the defeats of Serena Williams and Maria Sharapova.
It was a major scalp for Radwanska, who had lost all seven previous meetings with the Belarusian, and now goes into a semi-final with Slovak 20th seed Dominika Cibulkova.
The win also ensures the tournament will have a new champion with none of the semi-finalists -- Radwanska, Cibulkova, Li Na and Eugenie Bouchard -- having won before.
<img src="http://images.mid-day.com/images/2014/jan/radwanska22jan.jpg" alt="Radwanska" /> Radwanska after her win against Azarenka. Pic/ AFP
"It is always hard against her. I have lost so many times that (I knew) I had to play aggressive and go for my every shot. That's what I tried to do and it worked today," she said.
One of Radwanska's biggest challenges was to block out Azarenka's grunting, which has frustrated her in the past.
It came to head in Dubai in 2012 when the Pole said she was "angry" and had "lost a lot of respect" for the Belarusian because the noise coming out of her.
Fairfax Media said it had recorded a 90 decibel grunt in Azarenka's first round match -- louder even than renowned shrieker Sharapova.
Whatever the reason, Radwanska has always struggled against her. The pair, both 24, had met 15 times before with the Belarusian leading 12-3, winning their last seven meetings.
But the dam finally broke as Radwanska battled into her first semi-final in Melbourne, having made the quarter-finals four times before without going further.
Azarenka had not dropped a set all tournament, but 47 unforced errors cost her dearly to end her 18-match win streak at Melbourne.
The calm and collected Pole opened her account on Rod Laver Arena with an easy service game and then shocked the world number two by breaking her when she hoisted a forehand wide.
Radwanska fought off an Azarenka break point in the third to go 3-0 ahead, having forced eight errors from her opponent in the first three games.
In a pivotal fourth game, highlighted by some exceptional rallies, Azarenka fought off four break points before falling on the fifth when she sent a lob long.
The Polish number one kept the pressure on by serving to go 5-0 in front, pushing the second seed around the court. Azarenka finally got a game on her next serve but the set was lost.
Azarenka was struggling with her serve and needed to repel four break points in a 10-minute first game of the second set to hold.
She was not getting many chances and when she did, she was not making the most of them, throwing away two break point opportunities in the next game.
They both held for 2-2 and then an Azarenka double-fault gifted Radwanska two break points in the fifth game and she accepted the present by drilling a backhand down the line.
Her joy was short-lived as Azarenka broke straight back and then held to be 4-3.
It went with serve till 6-5 when the Belarusian finally pounced, blitzing a forehand winner to break and take the set.
But Radwanska showed grit to bounce back and come through a tense 11-minute game to get the break and a 1-0 lead in the third.
She held serve, then broke again for 3-0 with a frustrated Azarenka having no answers to the Pole's all-court game.

Two-time defending champion Victoria Azarenka was bundled out in the quarter-finals on Wednesday by fifth seed Agnieszka Radwansa in another big tournament upset

Australian Open: Radwanska knocks champion Azarenka out

Australian Open: Paes-Stepanek exit after quarter-finals loss

Two-time defending champion Victoria Azarenka was bundled out in the quarter-finals on Wednesday by fifth seed Agnieszka Radwansa in another big tournament upset

Australian Open: Radwanska knocks champion Azarenka out

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Australian Open: Radwanska knocks champion Azarenka out

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