Simona Halep said victories by Angelique Kerber at the Australian Open in January and Flavia Pennetta's US Open triumph last September had given the other players the belief that Serena Williams can be beaten.

Flavia Pennetta defeated Roberta Vinci earlier this year in the first ever all-Italian Grand Slam final to claim the biggest win of her career - the US Open, and then announced her retirement from the sport

Flavia Pennetta ended her three-year relationship with former world No. 1 Carlos Moya after he was allegedly found cheating on her with a TV presenter/model.

Flavia Pennetta, who will retire after WTA Finals, stayed on course for her one last title when she beat Poland's Agnieszka Radwanska 7-6, 6-4.

Top seed Simona Halep will be paired in the same group with Maria Sharapova and Flavia Pennetta in the season-ending WTA Finals.

Flavia Pennetta and Angelique Kerber join Simona Halep, Garbine Muguruza, Maria Sharapova, Petra Kvitova and Agnieszka Radwanska in the October 23-November 1 tournament in Singapore.

Flavia Pennetta could hardly find her rhythm facing Lyudmyla Kichenok and the top seed surrendered in one hour and 38 minutes

Apart from Flavia Pennetta, Martina Hingis, Sania Mirza, Kevin Anderson, Marcos Baghdatis are some of the top players who will compete in the Champions Tennis League, to be held from November 23 to December 6.

US Open champion Flavia Pennetta has jumped 18 places to be ranked eighth in the world as the top four remain the same with Serena Williams well clear of second-best Simona Halep.

Flavia Pennetta retired on Saturday only minutes after defeating compatriot and friend-since-childhood Roberta Vinci 7-6 (7/4), 6-2 in US Open 2015 final to become the oldest first-time women's Grand Slam champion.