(CNN) -- Petra Kvitova dumped Caroline Wozniacki out of the WTA Championships with a straight sets victory that sealed her place in the final four. 

Kvitova, the 2011 Wimbledon champion, inflicted Wozniacki's second defeat in Istanbul, winning 6-4 6-2 to go top of the Red Group. 

World number one Wozniacki, who called the trainer on during her match after complaining of feeling sick, is rock bottom of the group after playing all three of her round robin games. 

After her victory Kvitova told CNN she was delighted to make the final four: "It's nice when I win and I'm happy to be in the semi-final. Istanbul is a great place and it is great experience for me. 

"I have had a great season and it's very nice to play here -- it's like something new for me as I'm still learning. I am enjoying every match I play and I'm trying not to think about winning here." 

Wozniacki told reporters: "I tried my best, but my body didn't want to do the things I asked it today. What I told my brain didn't go to my body. 

"It's just unfortunate that my body has been feeling tired. To get sick now is not the best time if you want to beat the top players." 

Czech Kvitova faces Agnieszka Radwanska on Friday -- a match that will determine who grabs the second qualification spot in the red group. 

Radwanska, from Poland, currently occupies second spot after she saved three match points to beat Russia's Vera Zvonareva 1-6 6-2 7-5. The Pole can make sure of her place in the semis as long as she wins a set in her clash with Kvitova. 
Who spoke to CNN about her win?
How does she feel about being in the final four?
When did she win?
What did she become?
Who did she beat in Istanbul?
Who is ranked number one?
Was she feeling okay?
Who did she tell?
Where did she place in the Red Group?
Who had a good season?
Does she hate the sport?
How does she feel about playing?
What was wrong with Wozniacki's brain?
Who is ranked number two?
Where is she from?
Who did she win against to get placed second?
Where is she from?
Who will Radwanska play next?
When?
What place will the winner be in?
Kvitova
After her victory Kvitova told CNN she was delighted to make the final four
delighted
After her victory Kvitova told CNN she was delighted to make the final four:
2011
Kvitova, the 2011 Wimbledon champion
Wimbledon champion
Kvitova, the 2011 Wimbledon champion,
Wozniacki
Kvitova, the 2011 Wimbledon champion, inflicted Wozniacki's second defeat in Istanbul
Wozniack
World number one Wozniack
no
Wozniacki, who called the trainer on during her match after complaining of feeling sick
the trainer
Wozniacki, who called the trainer on during her match after complaining of feeling sick,
last
World number one Wozniacki, who called the trainer on during her match after complaining of feeling sick, is rock bottom of the group after playing all three of her round robin games. 
Kvitova
After her victory Kvitova told CNN she was delighted to make the final four: "It's nice when I win and I'm happy to be in the semi-final. Istanbul is a great place and it is great experience for me. 

"I have had a great season 
no
 I am enjoying every match I play
she enjoys it
I am enjoying every match
it didn't go to her body
Wozniacki told reporters: "I tried my best, but my body didn't want to do the things I asked it today. What I told my brain didn't go to my body. 
Radwanska
Radwanska, from Poland, currently occupies second spot 
Poland
Radwanska, from Poland
Vera Zvonareva
adwanska, from Poland, currently occupies second spot after she saved three match points to beat Russia's Vera Zvonareva
Russia
Russia's Vera Zvonareva 
Czech Kvitova
Czech Kvitova faces Agnieszka Radwanska on Friday
on Friday
Czech Kvitova faces Agnieszka Radwanska on Friday
second
a match that will determine who grabs the second qualification spot in the red group.