Additionally, Maria Sharapova - who had already qualified - announced she has to withdraw due to a right shoulder injury, which has limited her action in the second half of the season to only one match.
"I am very disappointed that I will not be able to play in the TEB BNP Paribas WTA Championships this year," Sharapova said. "The fans in Istanbul have welcomed us each year with such intense passion and warmth, I will sincerely miss the energy and excitement they brought to the year-end tournament. I want to thank Istanbul for being a tremendous host and hope to play in Turkey sometime in the future."
The Top 8 singles players and Top 4 doubles teams will compete in Istanbul for a record-setting $6 million prize money purse and the most prestigious title on the WTA calendar after the Grand Slams.
Only one spot in the eight-player singles field remains, and the four doubles spots are all filled up.
"As we prepare for the third and final set of the TEB BNP Paribas WTA Championships in Istanbul, I know having Jelena, Petra and Sara in our elite field will provide the passionate fans in Turkey with exciting and inspirational matches," WTA Chairman & CEO Stacey Allaster said of Monday's news.
Kvitova's 2013 season has been highlighted by her 10th and 11th WTA titles at Premier events in Dubai and Tokyo, and finals at Katowice and New Haven. This is the third year she has qualified for the WTA Championships, having done it in 2011 (winning the title) and 2012 (falling in the round robin).
"I am so happy to qualify for the TEB BNP Paribas WTA Championships again this year," Kvitova said. "To be among the best players in the world means a lot, especially after a tough start to this year. I'm so excited to return to Istanbul for the final year of the Champs there and looking forward to playing in front of the Turkish fans. I hope to continue my recent good form and play my best tennis there."
Errani's year has been highlighted by her seventh WTA title at Acapulco and three more finals at Paris [Indoors], Dubai and Palermo. This is the second year she has qualified for the WTA Championships, having done it in 2012 (falling in the round robin stage). Additionally, this is the second straight year she has qualified for both the singles and doubles events alongside fellow Italian Roberta Vinci.
Jankovic started the year outside the Top 20 and has worked her way back into the Top 10 - No.8 this week - after some very consistent results, including her 13th WTA title at Bogotá and two more finals at Premier events in Charleston and Beijing last week. This is the fifth time Jankovic has qualified for the WTA Championships - her best results have been a pair of semifinal showings in 2008 and 2009.
Following two successful, record-breaking editions, Istanbul hosts the WTA Championships for the third and final year in 2013. In 2012, the tournament attracted more than 73,000 fans during six days of competition, the highest attendance at the year-end event since 2000. Broadcast coverage reached 167 countries, and the overall hours produced increased 25 percent, including live matches, match replays and highlights. Nearly 42 million fans followed the on-court and behind-the-scenes action via WTA social media and digital platforms, and it was a record-setting week for the official WTA website that week, with approximately 4.8 million page impressions and nearly 500,000 unique visitors.