Novak Djokovic set up a semi-final with Roger Federer, the four-time US Open champ-ion, by defeating Andy Roddick in a high-class quarter-final - then was promptly booed by a partisan Flushing Meadows crowd.

The Serbian's emotions got the better of him in a court-side interview after his 6-2, 6-3, 3-6, 7-6 victory, when he hit back at the American's pre-match claims that Djokovic was faking injury. "Andy was saying that I have 16 injuries in the last match so obviously I don't, right?" said Djokoic. "That's not nice anyhow to say in front of this crowd that I have 16 injuries and I am faking it."

With the crowd in the Arthur Ashe Stadium booing loudly, he continued: "Like it or not, it's like that. They the crowd are already against me because they think I am faking everything, so sorry. I am really happy playing against Roddick on his court and in his city in his favourite tournament so to win against him is a huge effort."

Roddick felt Djokovic had over-reacted to something that had been a joke. "It was completely meant in jest," said the 2003 champion. "I'm sorry he took it that way. Maybe I did him a favour tonight."

Djokovic faces Federer tonight after the Swiss spared himself a repeat of his "dogfight" five-set win over Russian Igor Andreev, but his 7-6, 6-4, 7-6 victory over Gilles Muller, 130th-ranked Luxembourg qualifier, was not exactly the kind of performance one would have expected from a man who extended his unbeaten run at Flushing Meadows to 32 matches.

Good display or not, Federer hung in to advance to a record 18th successive grand slam semi-final. "I'm happy to keep the semi-final streak alive. That's a huge streak for such a long time," said the Swiss, who is aiming to become the first man since 1924 to win five in a row here.