Maria Sharapova heads into the WTA Finals with a lack of match practice as in-form duo Garbine Muguruza and Agnieszka Radwanska carry confidence in.
Halep has enjoyed an excellent year, but she comes into the Finals in questionable form. An Achilles injury led to her retirement in Beijing, having failed to go further than the quarter-finals (Guangzhou) on the Asian swing. The Romanian one-time grand slam runner-up has a semi-final (US Open) and quarter-final (Australian Open) appearance at majors this year.
Unlike Halep, Muguruza's form late in the year has been impressive. The Spaniard was runner-up in Wuhan before backing up to win Beijing, claiming the scalps of Ana Ivanovic, Angelique Kerber and Agnieszka Radwanska during her runs. The Wimbledon runner-up's power, mixed with confidence and form, is set to make her a threat.
The Russian comes into the tournament underdone. Her first appearance since Wimbledon was in Wuhan and she retired during the third set due to an arm injury. Five-time slam winner Sharapova has enjoyed an excellent year with just eight losses, but her lack of match practice may prove costly. She is without a win since reaching the semi-finals at the All England Club.
Kvitova has battled for form since the US Open, winning one of three matches since then. The two-time Wimbledon champion's straight-sets losses to Italian pair Roberta Vinci and Sara Errani in Wuhan and Beijing respectively make for worrying reading. The Czech left-hander's best performance at a grand slam this year was at Flushing Meadows, where she made the last eight, but she must recapture some form to threaten.
The Pole is in red-hot form heading into Singapore. Radwanska has enjoyed the Asian swing more than most, winning titles in Tokyo and Tianjin. There were few scalps in Tianjin, but she beat the likes of Elina Svitolina, Karolina Pliskova, Dominika Cibulkova and Belinda Bencic in Japan. Radwanska has the crafty game to trouble most and she is confident heading in.
The powerful left-hander has failed on the big stage this year, with a first-round exit at the Australian Open followed by third-round departures at the last three grand slams of 2015. There are no question marks over her talent, but whether she can put it all together against good players consistently remains to be seen. Kerber's form in Asia this year has been solid, but she has battled a back injury late in the year.
The US Open champion gets to bow out alongside the best. Singapore will mark the 33-year-old Pennetta's final tournament before retirement as she looks to go out in style. Pennetta's form since her success at Flushing Meadows has been scratchy in what has been a solid year made impressive by her maiden grand slam title.
An infection hospitalised Safarova in September in what has been a bad finish to 2015. Her first-round loss at the US Open was followed by disappointing performances in Linz and Moscow. The left-handed Czech is capable of troubling the best, with the highlight of her year a run to the French Open final.