Who of the eight WTA finalists in Singapore is Serena Williams' most likely successor?

It's been one of the most unpredictable years in the history of the WTA Tour, with 2017 providing four different slam winners (two of whom were unseeded), and five separate world No 1s. 

The WTA Finals in Singapore brings together the eight best players from the year, and should in theory provide some clues as to who could replace Serena Williams as a long-term world No 1 when the American eventually retires. 

Ahead of the tournament starting on Sunday, Telegraph Sport ranks the eight finalists by their prospects of dominating the game long-term. 

8. Venus Williams - current ranking No 5

This is of course no reflection on a magnificent career, but at 37 years old, even Venus must be thinking of retirement in the next few years.  

One final slam is probably a more realistic proposition than another extended spell at world No 1 for a player who has already established herself as a legend of the sport. 

That said it would be entirely in keeping with the Williams sisters incredible capacity for reinvention if Serena's successor at the top of the sport was her elder sister who she supplanted as the world's best 15 years ago. 

7. Caroline Wozniacki - current ranking No 6

Wozniacki deserves a huge amount of credit for clambering back into the world's top 10 after suffering a terrible dip that saw her ranking plummet to as low as 74 last year. 

But her ill-fated 67-week spell as world No 1 between 2010 and 2012 suggests she is probably not the future of the sport. Wozniacki's failure to win a grand slam became a cause célèbre during her time at the top of the rankings, and she has got no closer to winning a major in the last few years despite rediscovering her consistency elsewhere.

Wozniacki, 27, will likely extend her impressive record of having won a title every year since and including 2008, but her lack of power will prevent her from becoming the dominant force in women's tennis. 

6. Karolina Pliskova - current ranking No 3

The Czech, 25, has been ranked No 1 this year, but lasted just eight weeks and is yet to convince that she has what it takes to remain as the world's best long-term. 

After reaching the US Open final in 2016, her grand slam performances have been solid enough this year, save for a hugely disappointing second-round exit at Wimbledon where she was many people's favourite. 

The power Pliskova possesses - especially on what is a booming serve - will keep her competitive at the biggest events, but there are question marks over whether she has enough variety to consistently win majors. 

Until she breaks her slam duck, those doubts will remain.  

At a glance | WTA Finals

5. Elina Svitolina - current ranking No 4

An excellent year for Svitolina has seen the Ukrainian break into the world's top 10 for the first time and win five titles - two on clay and three on hard courts.

Svitolina, 23, has previously worked with Justine Henin and she shares some of the Belgian's cerebral shot-making skills. 

Over the course of 2017, Svitolina has beaten pretty much all of her fellow Singapore finalists, including Venus Williams, Garbine Muguruza, Simona Halep and Caroline Wozniacki in the space of one tournament at the Rogers Cup. Such has been Svitolina's consistency that she was within two matches of claiming the world No 1 spot at the US Open. 

Her lack of power and disappointing results at the grand slams so far mean a note of caution should be sounded, but Svitolina certainly has the shots to be a regular at the sharp end of majors in the coming years. 

4. Caroline Garcia - current ranking No 9

After watching Garcia tear into Maria Sharapova as a 17-year-old wildcard at the 2011 French Open, Andy Murray claimed that we were watching a future world No 1. 

Thus far Garcia has been far too inconsistent to get near the top of the rankings, but things have begun to fall into place for her this year. 

A run to the French Open quarter-finals was her best ever showing at a major, and she has since become the first woman to complete the China double by winning Wuhan and Beijing back to back earlier this month. 

A big change for Garcia this year has been to largely stop playing doubles and focus on the singles. She has also quit playing Fed Cup, which led to condemnation from her team-mates - not least former doubles partner Kristina Mladenovic - but may well prove to be a sensible decision in keeping her fresh for the biggest events. 

Still only 24, Garcia undoubtedly has a big enough game to become a future world No 1 if she can cut out the mental lapses that have occasionally plagued her. As she has shown over the last few weeks in China - where she has beaten the likes of Angelique Kerber,  Svitolina, Petra Kvitova and SimonaHalep - once she gets some momentum she can be an extremely dangerous player. 

Her evisceration of the world No 1 Halep in the Beijing final was especially eye-catching, and underlined just how good Garcia can be. 

3. Jelena Ostapenko - current ranking No 7

Ostapenko's career is probably the toughest on this list to try and forecast, since her all or nothing game means she could just as easily end up being a one-slam wonder as she could become a serial winner of major titles. 

One thing that is for certain is that the 20-year-old Latvian is hugely entertaining to watch. There are times when she resembles a gambler putting everything on red at the roulette table, and when it comes off it is similarly breathtaking. 

Her performance at the French Open in June where she bulldozed her way to the title with a barrage of ferocious forehands was staggering, not least for the fearlessness she displayed in even the most pressurised of moments. 

Ostapenko's ranking has climbed from No 47 before Roland Garros to a current high of No 7, and she has continued to demonstrate over the last few months that when she's hot there's not a lot her opponents can do.

Now those around Ostapenko face a dilemma. Should they encourage a bit more caution in her game to try and add some consistency to the drastic highs and lows, or would that risk tampering with the Latvian's child-like enthusiasm that seems to insulate her from the anxiety many of her opponents feel? 

Getting the balance right will be critical to Ostapenko's prospects, and if she can do that then anything is possible for a player with a harder forehand than many of her male counterparts. 

2. Simona Halep - current ranking No 1

Halep is in some respects everything that Ostapenko is not. Where Ostapenko came out of nowhere to win her maiden grand slam at the French Open, Halep - the losing finalist at Roland Garros - has been a perennial bridesmaid on the WTA Tour, never quite able to get over the line and win a grand slam. 

And where Ostapenko's game-style is all-out attack, Halep's greatest assets are her athleticism and defensive skills. 

Halep has also had her fair share of mental collapses over the last few years, so much so that her coach Darren Cahill temporarily left her side after receiving a torrent of on-court abuse during a painful defeat to Johanna Konta in Miami back in March.

It appears though as if Halep, 26, is starting to turn a corner in this regard. She is back working with Cahill after convincing the Australian the she will cut out the mid-match meltdowns, and crucially she finally claimed the world No 1 ranking by reaching the Beijing final. The relief at doing so was all the more marked because three times previously - including at this year's French Open final - Halep had lost when one win away from claiming top spot. 

Now the question that will dominate women's tennis is can Halep justify her world No 1 ranking by finally winning a grand slam? 

Should she get that monkey off her back at last, then it would be natural to expect others to quickly follow. But the longer Halep goes without claiming a major the worse the pressure will become, especially if she remains world No 1. Just ask Wozniacki or Dinara Safina. 

It is a personal view that Halep will eventually win a slam, and once she does then she has the consistency to remain world No 1 for some time. 

1. Garbine Muguruza - current ranking No 2

Garbine Muguruza positively shimmers with star quality. She plays with a poise and a power that can be irresistible, and off the court she is articulate and thoughtful. 

In short, she is everything the WTA Tour is dreaming about for the time when Serena Williams finally hangs up her racket and a new queen of the court has to be anointed. 

Muguruza briefly rose to the top of the rankings this year, but broadly speaking she has been held back by a lack of consistency. What she does possess though is an ability to rise to the big occasion in a manner that rivals even Stan Wawrinka.

Take her tournament form between June 2016 and July 2017 when Muguruza won just two titles - the French Open and Wimbledon. She did not even reach a final in between those two, and can give the impression that unless it's a grand slam match on a main show court, it's not worth getting out of bed for. 

As and when Muguruza gets the hunger to compete regularly for titles throughout the year - she admitted in July that she can struggle for motivation and has "a love-hate relationship with tennis" - she will surely start to dominate. 

There is also a degree of maturing that Muguruza, 24, still has to do. She has admitted that at times she has made errors by being unnecessarily aggressive because she hates the thought of being at the mercy of what her opponent does. This need to be the alpha-female at all times makes for thrilling tennis, but it can also mean Muguruza ends up beating herself in matches. 

Overall though, Muguruza looks to have everything in her armoury to be the WTA's dominant player for years to come. Her clean hitting has already earned her two majors - one on grass, one on clay - and if she can stay motivated then there will be many more to come.