Petra Kvitova continues to kick tail

Petra Kvitova and Victoria Azarenka entered the year-end championships as two of the hottest players on tour. They're still on course to meet in Sunday's final.

But before then in Istanbul, they'll have to get past a Grand Slam winner and two-time Grand Slam finalist intent on pulling upsets.

Here's a preview of both semifinals.

Petra Kvitova versus Samantha Stosur

A star might have been born when Kvitova won Wimbledon, but it's only now that the Czech is truly blossoming.

There are signs everywhere.

When Kvitova misses, a look of annoyance rather than resignation engulfs her face: She expects to make every ball -- and she expects to win. She remains a little shy off the court, but on it she had become bolder. Kvitova is easily much more comfortable in grand surroundings, knowing she's a main attraction.

Her newfound steel is demonstrated by that clenched fist prior to returning, a la another tall Grand Slam champion from Eastern Europe. If she keeps progressing at this rate, Kvitova will no doubt end her career with more majors than Maria Sharapova.

Kvitova's fate largely rests in her hands when she plays, and Friday's 7-6 (4), 6-3 victory against Polish battler Agnieszka Radwanska was a good example. Down 5-1 in the first set as the errors flowed, a flurry of winners got Kvitova back to 5-5 -- and quickly. She went undefeated in the Red Group, bringing her win streak to eight matches, and she is playing like a world No. 1.

Stosur won't be lacking confidence, either.

After all, she's also a Grand Slam champion and thrashed a completely frazzled Li Na 6-1, 6-0 on Friday to advance. Stosur's heavy kick serve provided the power, while her short backhand slices continually deceived.

But Stosur's kick serve is likely to land right in Kvitova's wheelhouse. Another problem for Stosur is that Kvitova usually goes cross court with her monstrous lefty forehand. If the pattern continues, it means a slew of balls to Stosur's backhand, her much weaker wing.

Unless Kvitova capitulates, the winning streak should linger.

Prediction: Kvitova in two

Vera Zvonareva versus Victoria Azarenka

It was all going so well for Zvonareva against Radwanska on Thursday.

She was ripping winners down the line, being aggressive at the right times and keeping cool against a wily opponent who'd beaten her three matches in a row. A downbeat, ailing Radwanska looked like she was ready to check out in an hour.

But when Zvonareva was broken early in the second set, she panicked. After wasting three match points, Zvonareva suffered one of the worst losses of her tumultuous career.

As down as she was, Zvonareva has a second chance. Her bags were probably packed when Radwanska, who needed just to win a single set to advance to the semifinals, took a 5-1 lead against Kvitova in the first set Friday. But we know how that played out.

The way this season has gone on the women's tour, you never know what might happen next. Zvonareva is 6-3 against Azarenka, one of the few players who possess a solid head-to-head record against the Belarusian. Zvonareva, who benefited from a day off Friday, suffered a bad loss to Azarenka in Miami the last time they played but has won two of the past three encounters.

Further, whenever Azarenka appears to be on the verge of something special, she can't see it through. As the favorite against Li at the French Open, Li prevailed, and as the favorite versus Kvitova at Wimbledon, Kvitova prevailed.

But is this finally a different Azarenka, one who can triumph at an important event -- outside Miami?

Azarenka has built on the momentum she collected in capturing a title last week in Luxembourg, breezing past Stosur and Li in straight sets this week.

With nothing to play for Friday -- excluding prize money, and she has enough of that -- Azarenka looked disinterested against alternate Marion Bartoli in a 5-7, 6-4, 6-4 loss that snapped her nine-match winning streak (which includes a walkover). She had no intention of winning the final set; Bartoli, as tennis fan pointed out on Twitter, exerted more effort on her famous practice swings. The fans didn't like it.

Etiquette aside, don't read too much into it.

When it really mattered, against Stosur and Li, Azarenka ascended to another level, serving well, dominating from the baseline and retrieving admirably. She's mentally tougher than Zvonareva, and motivation won't be in short supply Saturday.

Prediction: Azarenka in three