It’s common knowledge in tennis that the best strokes, the fastest feet, and the longest reach are of no use to a player with frayed nerves or little self-esteem. While the game may not require more mental fortitude than other professional sports, it offers no place to hide uncertainty. At least Yankees fans from years back could hope that slow grounders would not roll Chuck Knoblauch’s way; in tennis, the ball is always coming toward you, and you have to believe you can pound it time and again if you are going to win.

Though Nadia Petrova can’t match the talent of Justine Henin-Hardenne, the Russian yesterday proved even more inferior in terms of confidence in a 6-2, 6-3 semifinal loss. Petrova credited her opponent with playing a near perfect match; in truth, Henin-Hardenne didn’t come close to duplicating her virtuoso performance of a round earlier against Maria Sharapova. The Belgian double-faulted six times, made 23 errors, and twice lost her serve immediately after breaking for the lead. Yet Petrova managed to win only five games in an hour and eight minutes.

Rather than let loose on her forehand or charge the net with abandon, Henin-Hardenne sat back and played patiently. Petrova took care of the rest, committing 26 errors against only seven winners. On the penultimate point of the match, she decided not to swing at a ball on the line, thinking it was out.

Despite the quick victory, Henin-Hardenne said she is tiring and that her nagging leg and back injuries are not improving.

“I think I will have to give my best one more time and then take a rest,” the former world no.1 said.

In the other women’s semifinal, no amount of confidence would have helped Elena Likhovtseva overcome the 30-year-old Mary Pierce, who continued her impressive comeback with a 6-1, 6-1 win. Pierce simply hit Likhovtseva off the court, smashing 26 winners and only 11 errors.

Considering Henin-Hardenne’s physical struggles and the fact that she has played well only twice this tournament, Pierce, the hometown favorite, has a shot at the title on Saturday. Three sets will almost certainly be in order.

***

When Roger Federer and Rafael Nadal meet today in the most anticipated contest of the season, the world no. 1 will find himself in a curious role. Federer has lost just two matches this year and both were close affairs. Otherwise, he has run roughshod over his opponents, compiling 46 wins and collecting six titles. Yet in this semifinal, Federer is only the slight favorite, or perhaps an even-money bet.

“I think it’s 50 /50, basically,” Nadal said after his quarterfinal.

Nadal, who turns 19 today, is not being presumptuous about his chances. He certainly has the talent, the spirit, and the tenacity to prevail, as he proved at the Miami final earlier this year when he won two flawless sets and had the third in his grasp before Federer squeaked by in a tiebreaker and then pulled away.

That was on a hard court, and this is on clay, Nadal’s favorite surface. As well as Federer moves on clay, Nadal does it better. He also misses less frequently, owing to the incredible amount of topspin he hits on all his strokes, especially his forehand. Spin was key to Nadal’s success in Miami: Federer was not prepared for balls that bounced off the court as if they had been struck from five feet above the net. The fact that Nadal is left-handed only complicates matters.

This time around, Federer will be ready, and in the rare position of having something to prove. As he reminded the press this week, he is accustomed to success at this stage in Grand Slams and has not forgotten his semifinal loss to Marat Safin at the Australian Open. The Swiss has not dropped a set in this tournament even though, by his own admission, he has yet to play a great match. The implication is that he expects to play one, and soon.

If it happens today, Nadal – the king of the clay-court season and the most promising teen on the tour – will discover what it means to be no. 1. The only Grand Slam Federer has yet to win is within reach, and it’s difficult to imagine him going home without it.