Contorting his body while sliding into shots, Novak Djokovic used his typical relentless defense to reach the US Open semifinals for the seventh consecutive year.

Not quite as unflinchingly dominant as he was during his first four matches in the tournament, the top-seeded Djokovic quickly overcame a one-set lull on Thursday night against 21st-seeded Mikhail Youzhny of Russia before nailing down a 6-3, 6-2, 3-6, 6-0 victory.

Djokovic, the 2011 champion at Flushing Meadows, won the first 14 sets he played these two weeks, taking under two hours to advance each time.