Roger Federer struggled at times against 130th-ranked qualifier Gilles Muller before eventually winning 7-6 (5), 6-4, 7-6 (5) at the U.S. Open on Thursday to reach the semifinals for the 18th consecutive Grand Slam tournament.

It was Federer's 32nd victory in a row at Flushing Meadows, where he has won the past four championships.

Despite playing a man who never before was past the third round at a major, Federer had some trouble. He wasted six set points in the opener but closed it out on his seventh chance when Muller missed a backhand volley. Federer went 1-for-11 on break-point chances.

Bidding for a 13th Grand Slam title, which would move him one shy of Pete Sampras' record, Federer meets No. 3 Novak Djokovic or No. 8 Andy Roddick in the semifinals.