Tennis US OpenElena Dementieva, last year's beaten finalist at the US Open, had every reason to feel highly disgruntled after her 3-6, 6-2, 6-2 defeat by France's Mary Pierce yesterday. The Russian had dominated the opening set, and was then forced to wait 12 minutes while Pierce received a double medical time-out for a thigh injury and back problems.

It was all within the rules but surely against the spirit of tennis.

Pierce had tweaked her right thigh during her all-French quarter-final win over Amélie Mauresmo, although it was not strapped when she began the match, while her back has been a perennial problem.

First she had the thigh strapped, and then the back manipulated, while poor Dementieva did her best to stay calm and collected. However the rhythm she had built up in that first set was all but destroyed, while for the rest of the match Pierce showed no signs of being inconvenienced by either her thigh or her back. Her shots grew in conviction and she ran with freedom. So she became the first French woman to reach the US final.

These injury time-outs are now being abused by men and women players, and it is time the ITF, the world governing body, stepped in and changed rules for the slams. Currently they cannot interfere with what both the ATP and WTA do on their own Tours, but they could take a much-needed lead in the majors. If, on this occasion, Pierce was so badly hurt she could not continue, she should have been defaulted.

"I don't think it was fair play, but it was within the rules," said Dementieva. "I've never had such a long break before, but if that's the only way she can beat me then it's up to her. It's the way she plays. She always likes to take a lot of time between points, but I was a bit angry after that long break."

Of course, it can be argued that Dementieva, not the most mentally strong of players, should not have allowed the long break to affect her, and therefore did not deserve to win, something she tended to agree with.

The Russian has had dreadful problems with her serve and last year, in the French Open final which she lost to fellow Russian Anastasia Myskina, hit 10 doubles faults, and 67 in all in that tournament. It also cost her when she was beaten by Svetlana Kuznetsova in last year's US Open final.

Pierce has always been capable of hitting the ball as hard and cleanly as anybody, and the very fact she has been in five previous semi-finals, winning them all, and taking the Australian Open title in 1995,and the French Open in 2000, underlines her ability. The rejuvenation continues.

"Today, after I lost the first set, I just kept thinking about a friend of mine back at home, Pat, who's sick," said Pierce. "She just gave me the power to play today. I can't believe it. This is amazing. The fans really helped me."

Meanwhile, it is the essence of sport for everybody to search diligently for cracks and blemishes whenever a team or an individual becomes dominant for any length of time. And so, through the opening 11 days of this year's competition Roger Federer's form has been examined in minute detail. Was his serve a little awry? Was the forehand lacking its normal power? Was he struggling?

Before his quarter-final against the Argentinian David Nalbandian the world number one had dropped only one set. And if it was generally accepted the radiance was a little dimmed, most expected him to raise his game when the necessity arose.

This he did with a vengeance in the last of the men's quarter-finals, dismissing what had been billed as a lusty challenge from Nalbandian 6-2, 6-4, 6-1 with an imperious nonchalance. No male player in the Open era, dating back to 1968, has won back-to-back Wimbledon and US Open titles two years running. Federer, in all probability, will be the first.

Lleyton Hewitt won eight of his first 10 encounters with Federer between 2000 and 2003. Since then he has lost all eight of their meetings, including the 6-0, 7-6, 6-0 defeat in last year's final here, taking only two sets in the process. Today, Hewitt must convince himself the tide can be turned, just as the inexperienced American Robby Ginepri must believe he can defeat his country's living legend Andre Agassi in the other semi-final.