Belief the key for Kvitova against Serena

It all comes down to belief. Even when Serena Williams is not the world No.1 (it has been a sporadic problem), she still likes to think of herself as the world's best player. That is where she believes she belongs. Such confidence has brought her 12 grand slam titles (and counting) and has carried her through to the semi finals in SW19 for the seventh time.

Now that she, as the defending champion, has reached the last four, she must take on Petra Kvitova, the world No.62, who sounds, for all the world, like she does not believe at all. Beat the world No.1? Are you kidding? Take out the champion on Centre Court? Do me a favour.

Her response to the thought that only - and you have to love the use of that word "only" - Serena stood between her and a place in the final was to back away from the suggestion as quickly as possible. "She is very good player, and she won here I don't know how many times," Kvitova said. "I lost against her in the Australian Open. It was very quick. Yeah, I'm not favourite."

As for the thought that she could go on and win the title, that really was a joke. "No, I don't think, I don't think so, no," she said, laughing at the idea.

Then again, Yen-Hsun Lu never believed he could beat Andy Roddick either. And yet he did. A lack of confidence clearly did him no harm. Lu replaced his lack of belief with a willingness to fight - and Kvitova has shown that she certainly knows how to fight.

So to the nuts and bolts of the contest: the two have met once before, as Kvitova pointed out, and Kvitova could only win three games. That was on a hard court at the Australian Open but, then again, after a week and half of sunshine, the courts in SW19 are drying out and hardening up nicely so the conditions should not be dramatically different.

What will have changed hugely is the situation. In Melbourne, they met in the second round and both women knew their place: Williams was supposed to make her way to the sharp end of the competition while her Czech opponent was not supposed to delay her for too long. Both duly obliged.

Six months on and Kvitova has battered her way through the draw, knocking out seeds left and right. First it was Zheng Jie, then it was Victoria Azarenka and then Caroline Wozniacki. By the time she got to the quarter-finals, she had run out of seeds so, faced with Kaia Kanepi she pushed past her too.

All of her opponents so far have been able to wallop the ball and she, in turn, has absolutely pummelled the ball. Kvitova, then, should be ready for the power and pace of the champion on Thursday. What is likely to take her by surprise is the mental strength of Williams on a mission to win a major trophy. Williams simply refuses to tolerate the thought of defeat.

But Williams is also vastly experienced. The last person she expected to meet - or would have wanted to meet - was an out-and-out underdog with absolutely nothing to lose. With Kvitova's natural power, the last thing the champion needs is for the Czech to start swinging freely.

As a result, Williams was not celebrating her quarter-final win on Tuesday and she was not making predictions about her semi-final chances on Thursday - she had her game face on. And that does not bode well for Kvitova.

If Williams gets off to a quick start, she is liable to leave her rival for dust. If Kvitova can stand firm for the first set, she might just be able to push the champion. But, then again, maybe not.

Many women have tried to wrest a grand slam trophy from the grasp of Williams (did we mention that she is the defending champion?) and few have managed it. Williams has 12 gleaming Grand Slam replica trophies at home that prove that point rather nicely.