NEW YORK — Novak Djokovic heard what Andy Roddick said about him and didn't like it one bit.

Still, as much motivation as Djokovic might have had, and as well as he played in their U.S. Open quarterfinal tonight, Roddick's own uncharacteristic serving miscues had a lot to do with the 2003 champion's 6-2, 6-3, 3-6, 7-6 (5) loss.

Two points from forcing a fifth set at 5-4 in the fourth, Roddick double-faulted twice in a row and was broken for the fifth time — twice more than he lost serve in his first four matches combined.

In Djokovic's prior match, a five-set ordeal Tuesday against No. 15 Tommy Robredo, the reigning Australian Open champion called for the trainer more than once as he dealt with hip, ankle, stomach and breathing issues.

Asked then about Djokovic's problems, Roddick kidded around, checking whether the list shouldn't also include bird flu, anthrax, SARS and a common cold and said: "He's either quick to call a trainer or he's the most courageous guy of all time."

Roddick also said in an on-court interview that day: "I've got to feel good. He's got about 16 injuries right now."

After beating Roddick, ending the match with a 125 mph serve that drew a long return, Djokovic made reference to those comments.

"That's not nice anyhow to say in front of this crowd that I have 16 injuries and that I'm faking," Djokovic said during a postmatch interview that drew boos from the spectators in Arthur Ashe Stadium.

"They're already against me, because they think I'm faking everything."

The third-seeded Djokovic advanced to a semifinal meeting against Roger Federer. It's a rematch of last year's U.S. Open final, which Federer won for his fourth consecutive title at Flushing Meadows.

Federer beat qualifier Gilles Muller 7-6 (5), 6-4, 7-6 (5) Thursday, extending his own record by reaching the semifinals at an 18th consecutive Grand Slam tournament.

Djokovic is 2-6 against Federer and called him the "absolute favorite."