Agnieszka Radwanska Australian Open
Agnieszka Radwanska fires a forehand during her quarterfinal against Victoria Azarenka in the Australian Open, 22 January. Reuters

Upsets seem to be the order of the day at the Australian Open.

Serena Williams, Maria Sharapova and Novak Djokovic have all been shown the door in the first Grand Slam of the year in Melbourne, and the women's defending champion Victoria Azarenka has now gone through that same door after being outclassed by a brilliant Agnieszka Radwanska on Wednesday.

The petit Pole was in her elements against the favourite for the title, following Williams and Sharapova's departures, with Azarenka, despite a brief fightback, unable to provide any real answer, eventually going down 6-1, 5-7 and an emphatic 6-0 in the quarterfinals.

In the first last-eight match on Wednesday, Dominika Cibulkova, the woman who knocked Maria Sharapova out in the fourth round, continued her dominant run, easing past No. 11 seed Simona Halep of Romania 6-3, 6-0.

"I'm really glad with the way I played, especially with the way I handled it mentally," Cibulkova said after the easy win. "It was a big win against Maria. But I wasn't favourite in this match again against Halep, you know."

Cibulkova, seeded 20, admitted the triumph over Sharapova had indeed helped her to rise on the big occasions and see off any challenge from Halep.

"I know how well Simona playing," the Slovakian said. "She's running a lot of, giving a lot of balls back. I knew I have to be aggressive enough.

"But sometimes it's not easy because sometimes when you go for too much, it's too many mistakes. I knew I had to step into the court and play a lot to her weaknesses, use my backhand down the line that she was not expecting, to play some unexpected shots.

Dominika Cibulkova Australian Open
Dominika Cibulkova is over the moon after defeating Simona Halep in the quarterfinals of the Australian Open, 22 January. Reuters

"[She] reads the game very well. Even if you play well, you play fast, she's there at the ball.

"I walked on the court with the confidence that I can do it again today. I was so focused about what I have to do, to do the right things. That was all what I wanted to do, and of course enjoy my tennis again.

Cibulkova will no doubt face a real tough test against Radwanska, but the Polish No.5 seed will also know she will be in for a difficult match as well.

"If you play against the best players, you cannot do the same things all the time," Cibulkova added. "They know if you serve T and you give them two aces, so she's going to stand there next time.

"You have to change sometimes the tactics. When you go for the winner, I cannot go into the same spot.

"Of course it's less pressure [against Radwanska], even if it's not less pressure to play against big names.

"But now, it's the quarterfinals, semifinals. In the end of the second week of the Grand Slam. Nothing is easy. There is pressure you can feel from everywhere.

"So, I still want to do the same thing what I came into the tournament. I want to really enjoy it. I want to play my tennis. That's when I play my best."