Who's the favorite to win Istanbul?

The year-end championships promised so much.

At the start of the season, it wouldn't have been unfathomable to think that Serena Williams, Kim Clijsters and Justine Henin -- with their combined 24 major titles -- would qualify for the WTA Championships in Istanbul.

But none of the three are in Turkey, significantly lessening the star power. The lone multiple Grand Slam champion is Maria Sharapova.

What it means is that it's a wide-open tournament.

Here's a breakdown of the two groups after Sunday's draw.

Red (Caroline Wozniacki, Petra Kvitova, Vera Zvonareva, Agnieszka Radwanska)

Caroline Wozniacki

2011 record versus field (not including retirements): 2-3

The season began in somewhat controversial fashion for Wozniacki. At the Australian Open, she fibbed about encountering a kangaroo. Intended as a bit of fun, Wozniacki later had to set the record straight.

On the eve of the WTA Championships, there's more. After boyfriend Rory McIlroy dumped longtime agent Chubby Chandler, Chandler, speaking to the Daily Mail, speculated that Wozniacki might have had something to do with it. Even if it isn't true, it won't help her preparation.

Wozniacki was mediocre during the Asian swing, not reaching a semifinal. She didn't appear to be going through the motions, either.

Physically, however, she's had ample time to recover and continues to be a threat -- outside majors.

Petra Kvitova

2011 record versus field (NIR): 7-3

Who says small tournaments in the fall aren't important? The WTA event in Linz, Austria, could prove to be one of the most crucial stops for Kvitova in 2011.

Playing with a "free mind," Kvitova gained some much-needed confidence by winning the title and dropping only one set.

Her post-Wimbledon slump is officially over.

Linz was another example of the Czech lefty's still massive upside. No matter the opponent, when she's on, she's almost unstoppable.

Vera Zvonareva
2011 record versus field (NIR): 4-9

The pull for Russians to play at Moscow's Kremlin Cup is substantial, even if a few familiar faces opted for Luxembourg last week. Never having won her hometown tournament in 10 previous tries, Zvonareva wasn't about to skip the event and focus on Istanbul.

Maybe she should have.

As the top seed, Zvonareva lost to eventual champion Dominika Cibulkova in the quarterfinals. More worryingly, she needed treatment for a shoulder injury during their slugfest.

Zvonareva's first serve can just about get her free points -- at the best times -- but if the shoulder is sore, uh-oh.

Agnieszka Radwanska
2011 Record versus field (NIR): 4-6

It's hard not to like Radwanska. In an era of one-dimensional baseliners, she possesses variety.

Radwanska isn't afraid of going to the net; she changes pace and is a thinker.

The Pole rarely fusses and is a fighter, too. Coming off foot surgery, doctors didn't give her much chance of competing at the Australian Open. She not only made it to Melbourne, but landed in the quarterfinals.

Radwanska is one of the hottest players on tour, with her surge in Asia earning her the eighth berth in Istanbul. But will it be enough to overcome the elite?

Radwanska has beaten Zvonareva three times in succession but is a combined 1-5 versus Wozniacki and Kvitova.

Red group prediction: Kvitova first; Wozniacki second

White (Maria Sharapova, Victoria Azarenka, Samantha Stosur, Li Na)

Maria Sharapova
2011 record vs. field (NIR): 4-4

Sharapova injured her ankle in Tokyo and it isn't 100 percent yet, but she still decided to play in Istanbul. It's been four years since she competed at the year-enders, and she didn't want to miss out again. Sharapova arrived nice and early, allowing her to get used to the conditions.

How the ankle holds up is the undeniable issue for Sharapova, who has had a mostly uplifting season. The negative has been not being able to produce at crunch time in Slams.

As far as her double faults, what about this theory? With the ankle on her mind, maybe she'll dwell less on her serve and hit fewer doubles as a result.

Victoria Azarenka
2011 record versus field (NIR): 3-5

That Azarenka is still standing is a surprise.

In 2011, hip, shoulder, elbow, thigh, hand and foot injuries forced her to retire, give an opponent a walkover or pull out of a tournament altogether. (No knee?)

Azarenka was fit enough to play in Luxembourg and cruised to the title, going past the one-hour, 20-minute mark once -- in the first round. Hard courts are Azarenka's best surface, and she's 8-1 in her past nine on hard against her fellow group participants.

Samantha Stosur
2011 record versus field (NIR): 7-4

To say that Stosur put it all together this season would be an overstatement. Statistically, she had a better campaign in 2010 -- heading into the year-end championships. This year, the Aussie put it all together at a massive tournament, the U.S. Open, to become the latest first-time winner at a Slam.

She'll take the trade-off.

More experienced than Kvitova and calmer than Li, Stosur hasn't collapsed in the wake of her victory in New York. Losing twice to the feisty Maria Kirilenko is no shame, and Stosur rebounded by reaching a final in Osaka earlier in October.

Stosur owns Li (5-0). That's the good news. The bad is pretty bad. She's a combined 0-13 against Sharapova and Azarenka.

Li Na
2011 record versus field (NIR): 5-4

We all waited to see how Li would respond after winning the French Open.
Most felt it was right, tennis-wise, for her to not go back to China following her historic fortnight. Li and her team wanted to focus on Wimbledon instead, trying to keep out any and all distractions.

But since a tough second-round loss to Sabine Lisicki at the All England Club, things have gone downhill. She's won five matches since the French, had to bail from Tokyo with a knee injury and enters Istanbul with a three-match losing streak. As she's admitted, the pressure got to her. Cutting ties with coach Michael Mortensen, a steadying influence, added to the turmoil.

Low on confidence, winning a match would count as success.

White group prediction: Azarenka first; Sharapova second
Final: Kvitova def. Azarenka

London-based Ravi Ubha covers soccer and tennis for ESPN.com. You can follow him on Twitter.