How many times have you seen a tennis match less interesting than a press conference? Not many, I would guess. It was very interesting to witness the last quarter-final match of the 2008 US Open between Novak Djokovic and Andy Roddick and see a flat match compared to their battle of words which highlighted Day 12 in Flushing Meadow.

Perhaps the American shouldn't have "Djoked" about the world No.3.

Maybe Roddick will think twice about playing the schoolyard bully and picking on the guy with spiked hair who spends too much time in the nurse's office. Or, in his case, calls the trainer to the court more often than most.

During his five-set victory over Spaniard Tommy Robredo in the fourth round on Tuesday night, Djokovic was treated for everything from right-hip pain to a rolled ankle to a tummy ache. Following his round of 16 win over Fernando Gonzalez later that night, Roddick couldn't help making fun of his quarter-final opponent, suggesting Djokovic was also suffering from a cramp, the bird flu, a Beijing hangover (Djokovic lost in the semi-finals to Rafael Nadal but took the bronze medal), anthrax, SARS - even the common cough and cold.

Well, who's laughing now, Big Boy?

Playing with the ferocity of a wounded lion, but never asking for medical attention, Djokovic roared past Roddick 6-2, 6-3, 3-6, 7-6 in two hours 34 minutes to reach his second consecutive semi-final here. Last year, he fell to Roger Federer in his first major final.

Federer will be his opponent in the semi-finals tomorrow by virtue of a 7-6, 6-4, 7-6 victory over qualifier Gilles Muller of Luxembourg earlier yesterday. Federer has won six of their eight meetings, but Djokovic beat him in straight sets in the semi-finals of the Australian Open in January. Should Djokovic win tomorrow and go on to win the tournament, he would overtake Federer for the No.2 world ranking behind Nadal. Nadal, the top seed here, plays Scotsman Andy Murray in the other semi.

"Andy (Roddick) was saying I had 16 injuries in the last match, so obviously I don't," Djokovic shot back after the American sprayed a final forehand return of a serve long. "That's not nice to say in front of this crowd that I have 16 injuries and I'm faking."

From the outset, Djokovic played like a man on a mission. He met Roddick ace for ace, though Roddick did top out at 142 miles per hour. Djokovic was five for five on break points converted. Coming into the match, Roddick had dropped serve just three times in four matches; Djokovic broke him four times in the first two sets.

Roddick did manage to break in the third set, drawing hoots and hollers from the sellout crowd of more than 23,000. When he plopped into his chair, up 4-1 in the third, a huge grin crept across his face. Roddick ended the third set with four straight aces.

But almost as if he was the school principal, saying, "Wipe that silly grin off your face, young man," Djokovic stormed back from 5-3 down in the fourth, drawing to 5-5, then forcing a tiebreaker. Up five points to three, Djokovic netted a forehand, then smacked himself in the head with his racket. Roddick then pulled to 5-5 with a 142mph service winner, but Djokovic caught the crucial mini-break with a spectacular defensive side-to-side rally that Roddick tried to end with an unsuccessful drop shot. One point later, with a forehand return long, it was over.

"It was completely meant in jest," Roddick said of teasing Djokovic, who took heat for lighthearted imitations of other players, including Nadal and Maria Sharapova. "I decided to make light of the situation. I don't know if he took it seriously. If you're going to joke and imitate other people, then you've got to take it. I've been the worst of it in the past.

''By no means am I being holier than thou. I'm sorry he took it that way. There's nothing else to say. I don't think I went over the line. Maybe I did him a favor tonight."

Either Federer truly believes he is playing top-form tennis or the four-time defending US Open champion is playing a mind game nearly as potent as the one he displays on court. The No. 2 seed played reasonably well in defeating Muller. He has reached 18 consecutive semis in the majors, a staggering record in pro tennis. The last time he lost before the semis was in the third round of the 2004 French Open to three-time champion Gustavo Kuerten.

Although Federer managed to get through the match in straight sets, he was taxed by the 130th-ranked Muller, who upset fifth-seeded Russian Nikolay Davydenko in the round of 16. There were no breaks of serve in the first set, though Federer held five set points on Muller's serve in the 12th game, failing to consolidate any of them.

"It was tough today, especially to break against the wind," said Federer. "Look, I'm happy I won, first of all. This was a tough opponent who has been playing very well this tournament and, you know, showed why he was so dangerous today."

Federer's match statistics indicated a dominating performance. Although Muller had 16 aces to seven for Federer, the former world No.1 hit 42 winners and had 19 unforced errors. But his shots off the ground lacked the punch and joie de vivre fans have grown accustomed to, and his "wow" factor has barely been in evidence in the tournament.

He must play better to have any chance at beating Nadal, the man who took his No. 1 ranking before the tournament, should they reach Sunday's final. If Federer fails to win here, it would be the first time since 2002 he has gone winless in the majors.

When Federer finally closed out the two-hour-26-minute match, he thrust his hands downward and emitted a bellow that Tarzan would have envied. His show of emotion was uncharacteristic, especially this early in a tournament.

"Look, I'm in good spirits at the moment," said Federer, who lost in the quarter-finals at the Beijing Olympics to James Blake but won the gold medal in doubles with Stanislav Wawrinka. "Maybe I'm more outgoing [on the court] because I'm always like this in practice. Maybe it's a time where I can show a little bit more and it comes out."