After losing to Flavia Pennetta in the quarterfinals of the China Open, Caroline Wozniacki is under threat to lose her No. 1 ranking at the end of the year, although it is unlikely.
Four players still have a shot to unseat the Dane: No. 2 Maria Sharapova (who is considered questionable for the WTA Championships in Istanbul), No. 4 Victoria Azarenka, No. 5 Petra Kvitova and No. 6 Li Na.
Sharapova, who suffered an ankle injury in Tokyo, has the best chance of passing Wozniacki. There are seven different scenarios where it could happen, but only one of those has Sharapova just having to reach the Istanbul final, and the other six have her being forced to win the title.
The other three players are even bigger long shots. According to the WTA, Kvitova has to win the title in Linz and have Wozniacki lose all three of her round-robin matches in Istanbul; Azarenka has to win Luxembourg, hope that Wozniacki pulls out of the Championships (thereby receiving a zero-pointer in her ranking) and win the Championships; Li has to win both Moscow and the Championships, and hope that Wozniacki loses all three of her matches in Istanbul.