Wozniacki has heart, but her journey ends

Thursday turned out to be quite an eventful day at the year-end championships. Victoria Azarenka and Petra Kvitova advanced to the semifinals, while an ailing Caroline Wozniacki's journey ended.

Already without Serena Williams and Kim Clijsters, the final four won't include Woz or the other marquee name in the field, Maria Sharapova. Organizers must be happy, eh?

And in the match of the tournament, Agnieszka Radwanska took advantage of Vera Zvonareva's choke, er, nervousness, to keep her own chances of progressing alive.

Here's what we learned about each of the six players in action.

Petra Kvitova def. Caroline Wozniacki 6-4, 6-2

Wozniacki has a giant heart

Wozniacki has had a long, long season. Much of that, mind you, is thanks to her and her entourage. She plays way too much, exhibitions included, and her off-the-court diary always appears to be booked. The world No. 1 can't stand still.

All that said, however, Wozniacki deserves plenty of credit for the way she handled herself against Kvitova. Feeling unwell -- her pulse and blood pressure were taken early in the second set -- there was no retirement. Did you see that, Vika?

Rest up, Caro, and try to land that first major. The task will be even harder in 2012.

Kvitova's one wild ride

You can't take your eyes off Kvitova. Who knows what's coming off her racket next?

When the Czech misses, she does it with oomph. Kvitova almost clubbed Wozniacki with a drive volley that sailed long and hit a backhand volley that nearly made it to the backboard on the fly. One of her serves landed near the baseline, and an easy-looking forehand smash (or was it a volley?) hit none of the court.

Fortunately for the Wimbledon champion, she kept the misses to a minimum. Irrespective of Wozniacki's health, if Kvitova is on, the Dane doesn't have much hope.

Victoria Azarenka def. Li Na 6-2, 6-2

Vika's coach is pretty good

When Li beat Azarenka in the French Open quarterfinals, she pounded Azarenka's second serve. Seventeen points played -- and only six won by the Belarusian. Her coach, Sam Sumyk, was no doubt aware of that.

So what did Azarenka do Thursday? She made sure her first-serve percentage was up there. Taking the pace slightly off, it finished at 80. In the first set alone, it was 89.

Sumyk already has worked wonders with Azarenka's temperament -- the most aggression she shows now is in her scary, celebratory postmatch windmill fist pump -- and has the Frenchman turned Vika into Rafa II? Some of her scrambling was outstanding.

It's adding up to a Vika-Petra final.

Li's a confident player

When Li won the first set against Sharapova on Wednesday, her body language changed for the better. Not surprisingly, her game picked up. Sharapova's ankle injury gave her a further boost.

But after dropping the first set against Azarenka, you knew there was no coming back. Still lacking confidence, despite topping Sharapova, Li doesn't have the ability to grind out matches -- at least right now. Li fell to 4-12 in encounters where she's conceded the opening set this year and is 0 for her past 7.

Expect it to worsen to 0-for-8 when Li confronts Sam Stosur in their group finales; Stosur leads their head-to-heads 5-0. The winner lands second place in their group.

Sacking Michael Mortensen was a big mistake.

Agnieszka Radwanska def. Vera Zvonareva 1-6, 6-2, 7-5

Zvonareva is still a work in progress

How, oh, how did Zvonareva lose this match?

Even before blowing three match points in the third set, she made things too difficult for herself. Radwanska looked listless and helpless in the opening set, her heavily strapped right shoulder continuing to cause problems.

Zvonareva was in total control until she suddenly switched off early in the second. From then on, Radwanska gained belief. Zvonareva's own belief dipped, and so did her game. The killer instinct was missing. She made 55 unforced errors and stopped going to the net, a tactic so successful in the first.

There is a positive, though. Zvonareva didn't explode on court a la her 2009 collapse against Flavia Pennetta at the U.S. Open. Rather, she tried to smile away her frustration.

Radwanska never quits

Maybe Zvonareva's swoon had something to do with her recent record against Radwanska -- she'd lost three in a row, all since the U.S. Open Series.

Radwanska saved her best stuff for the final set. No wonder the crowd was on its feet after she saved the third match point with nothing but hustle.

Unfortunately for Radwanska, up next is Kvitova, who could feast on Radwanska's modest serves.