Novak Djokovic Vs Roger Federer : US Open 2008 semi-final

Third seed Novak Djokovic battled past Andy Roddick in four sets to confirm a meeting with defending champion Roger Federer in the US Open semi-finals.

The 21-year-old Serb was easing towards the last four when he claimed the first two sets in just 62 minutes but Roddick came from nowhere to take the third.

The 2003 champion served for the fourth at 5-4 but Djokovic forced a tie-break and came through 6-2 6-3 3-6 7-6 (7-5).

Federer, meanwhile, beat Gilles Muller of Luxembourg 7-6 (7-5) 6-4 7-6 (7-5).

The world number two will meet Djokovic for the third time in Grand Slams and just under a year on from their clash in the 2007 US Open final.

The Swiss prevailed that day to win his fourth successive title but has not won a Grand Slam since and has been replaced as world number one by Rafael Nadal.

"He's the absolute favourite," said Djokovic. "I lost to him last year and for him it's a big challenge to go back to number one. It's going to be a great match.

"I won against him this year in the Australian Open, that was my best tournament of the career, and against him that was one of my best matches.

"Hopefully I can do the same. I just need to be myself and need to be aggressive."

After being taken to five sets by Tommy Robredo in the fourth round, Djokovic looked set for a far quicker passage against an initially out-of-sorts Roddick.

The American, who struggled terribly on serve in the early stages, had no answer to his opponent's power, placement and variety from both the baseline and at the net.

Djokovic was forcing a litany of unforced errors out of Roddick, breaking serve in games two, four and eight to canter through the first set in 27 minutes.

Roddick was slowly establishing his rhythm but Djokovic broke for a 5-3 lead and deservedly wrapped up the second.

Cheered on by a partisan home crowd, eighth seed Roddick eventually found consistency on his own serve and began challenging Djokovic's, which enabled him to break for a 3-1 lead.

All of a sudden Djokovic's game was crumbling and Roddick's growing confidence resulted in an audacious passing shot to break for a 4-3 lead in the fourth set.

It appeared as though the match was destined for a fifth set but Roddick served two double faults when 5-4 and 30-0 up. Djokovic worked a break point and won the game by landing a lob on the baseline.

The Australian Open champion looked on top throughout a pulsating tie-break and completed the win when Roddick went long.

"There's not a whole lot of regret about how I played those last two sets," said Roddick. "I dug myself a hole and I gave myself a chance to get out of it but it was too little too late."

Djokovic will replace Federer as world number two if he wins the title at Flushing Meadows but the 12-time Grand Slam winner looked in good form against Muller, a qualifier.

Federer, who has not lost a match at the US Open since 2003, had to be patient and relied on raising his game at key moments rather than overwhelming his opponent as he may have done in the past.

The world number 120 survived Federer's first flurry, saving five set-points in the 11th game of the first set, but Federer struck decisively at 4-4 in the tie-break to close out the set.

Muller, the surprise package of the tournament, continued to serve strongly in the second set but, again, Federer chose his moment to pounce - breaking at 4-4 and serving out to extend his lead.

Federer never looked like being broken during the third set but he had to wait for another tie-break before sealing his victory.

This time Muller looked well-placed, leading 4-1 and 5-3, but two mistakes on serve proved crucial and Federer won four straight points to progress.

Federer's victory extended his US Open winning streak to 32 matches and his consecutive Grand Slam semi-final sequence to 18.

"I'm really happy with the way I pulled it out at the end because I thought it was going to four sets," said Federer.

"It's great to keep the semi-final streak alive. That's a huge streak for a long time. I'm really happy with my mindset going into the semi-finals."

The world number two is seeking a 13th Grand Slam title to move within one of Pete Sampras's all-time record.

He has triumphed in six out of eight meetings with Djokovic, including last year's US Open final, and has a 15-2 record against Roddick.

The other men's semi-final involves Britain's Andy Murray and world number one Nadal, who is seeking his third Grand Slam in a row after beating Federer in the French Open and Wimbledon finals.

Both semi-finals are scheduled take place on Saturday.