FLUSHING MEADOWS, N.Y. -- Serbian Novak Djokovic, bested fan-favorite Andy Roddick in a four-set thriller under the lights at Ashe Stadium.

Reigning four-time champion Roger Federer was also a hard-fought quarterfinal winner Thursday at the U.S. Open. The Swiss superstar will now play in his record 18th straight major semifinal against.

The second-seeded former world No. 1 Federer held off qualifier Gilles Muller of Luxembourg 7-6 (7-5), 6-4, 7-6 (7-5) on Day 11 on the hardcourts at the USTA Billie Jean King National Tennis Center.

Federer took the first set via tiebreak against the 6-foot-5 big-serving Muller, as neither player was able to record a service break in the opening stanza.

In the second set, the Swiss would assume control of the bout by registering the first, and only, break of the match for a 5-4 lead and then closed out the stanza with a hold for a commanding two-sets-to-love advantage.

The third set went to another tiebreak, which Federer captured by winning five of the last six points. He converted on his first match point when a game Muller netted one final backhand.

Muller swatted 16 aces in the 2-hour, 26-minute affair.

Federer is now 3-0 lifetime against the 130th-ranked Muller, with their previous two meetings coming in 2005.

The upstart 25-year-old Muller upset fifth-seeded Russian Nikolay Davydenko, 18th-seeded Spaniard Nicolas Almagro and former top-10 star Tommy Haas at this Big Apple fortnight. He overcame two-sets-to-love deficits against both the German Haas and Almagro.

Federer was this year's Wimbledon and French Open runner-up to Spanish stalwart Rafael Nadal, who supplanted the Swiss atop the men's rankings last month.

The 27-year-old Federer will see a familiar face in the semis on Saturday, as Djokovic looks to avenge last year's loss in the finals to the 12-time major titlist.

The Serbian star overcame a hostile crowd and a gutty performance from Roddick, topping the eighth-seeded American 6-2, 6-3, 3-6, 7-6 (7-5) in just over 2 1/2 hours.

Roddick, who was the last player to hoist the trophy (2003) before Federer's four-year reign, had no answer for the third-seeded Serbian's serve throughout the match.

After taking the first two sets with relative ease, Djokovic, who bested 15th- ranked Tommy Robredo in a five-set marathon in the quarterfinals, dropped the third set to Roddick.

The American looked to take control of the match, breaking Djokovic at 3-3 in the fourth and serving for the set at 5-4. But the Serb broke Roddick in the game and managed to force a tiebreaker.

At 5-5 in the tiebreak, Roddick tried to mix up a long baseline exchange with a drop shot, but his effort fell into the net and his return of Djokovic's serve on match point went long, much to the crowd's displeasure.

Djokovic topped Federer in the semifinals of the Australian Open earlier this year before taking Jo-Wilfried Tsonga for his first career Grand Slam title.

Saturday's other semi will pit the five-time major champion Nadal against sixth-seeded Brit Andy Murray, as those two men won their quarterfinal matches here on Wednesday. The 21-year-old Murray will appear in his first-ever Grand Slam semi.