Four-time defending champion Roger Federer advanced to his 18th consecutive Grand Slam semifinal on Thursday, stretching his US Open win streak to 32 matches and moving closer to a 13th Slam crown.

The Swiss second seed, who last missed a Slam semifinal at the 2004 French Open, defeated 130th-ranked qualifier Gilles Muller 7-6 (7/5), 6-4, 7-6 (7/5) to end a dream run by the Luxembourg left-hander.

"I'm happy to keep the semifinal streak alive. That's a huge streak for a long time. I'm really happy with my mindset going into the semi-finals. I'm happy to take it to the final four one more time," Federer said.

Federer next faces the Serbian sensation Novak Djokovic, whom he leads 6-2 in head to head competition.

The Serb blunted the big-serving American and 2003 champion Andy Roddick 6-2, 6-3, 3-6, 7-6 (5) in their quarterfinal encounter late on Thursday night.

The other men's semifinal will send British sixth seed Andy Murray against Spanish world number one Rafael Nadal, who seeks his third Slam crown in a row after beating Federer in the French Open and Wimbledon finals.

"Hopefully I can take it one more step than I did at the French Open and Wimbledon," Federer said.

The Swiss ruled the rankings for 237 weeks until last month, when Nadal ended his reign before capturing singles gold at the Beijing Olympics.

"You could see why he was number one," Muller said. "Every time the score was tight he came up with the better shot."

Aura of invincibility

Federer, 27, has not lost at the US Open since David Nalbandian beat him in the fourth round in 2003. But his aura of invincibility has been punctured this year after seasons of utter domination.

"It's not too much about Roger's invincibility. He's human. Everyone knew he had a tough year. He struggled a little bit. It's more the belief I had in myself, the confidence that I could beat him. I could have won the two tie-breakers for sure. I just wasn't so lucky," Muller said.

Federer won the only break of the match in the ninth game of the second set on a forehand winner. Muller denied Federer on three break points in the third set on the way to a tie-break, then grabbed a 4-1 edge before Federer rallied.

"It was really difficult - the sun, the wind and he was serving great," Federer said. "That's why straight sets is the best result."

Federer blasted a backhand winner to grab his first match point at 6-5 and Muller netted a backhand to end matters after two hours and 26 minutes.

"I'm happy I was able to come back and pull it out because it looked like it was going to go four," Federer said. "When you are down you try to fight and that's what I tried to do out there."

In the first tie-breaker, Federer rescued several shots in a long rally and then fired a backhand winner to grab a 6-4 lead.

Muller, who has spent more than four hours longer on the court at the Open than Federer, answered with a service winner but sent a backhand crosscourt volley wide on the next point to give Federer the set.

"He showed why he was so dangerous. It was hard just to get solid contact on his serve. It was the same for him for a while. There was not much rhythm out there," Federer said.

Muller, who twice rallied to win here after losing the first two sets, upset Russian fifth seed Nikolay Davydenko in the fourth round to become the second qualifier in the US Open final eight after France's Nicolas Escude in 1999.

"A lot of people think I should be happy, but I'm disappointed because I feel like I had my chances and I didn't take advantage of them," Muller said.