Fourth seed Novak Djokovic beat Spain's Fernando Verdasco 7-6 1-6 7-5 6-2 to reach his third consecutive U.S. Open tennis semi-final.
Both players struggled to find their timing in cool, blustery conditions with unforced errors more numerous than cleanly hit winners but it was Serbia's Djokovic who proved more solid.
Verdasco enjoyed a seven-game hot streak when his fearsome forehand clicked into gear but just when it appeared he was taking control of the quarter-final he faded away.
Djokovic, the 2007 runner-up, broke crucially at 5-5 in the third set courtesy of a rash forehand volley by Verdasco at deuce and cruised through the fourth set as Verdasco appeared to struggle with a stomach muscle injury.
Djokovic will meet either Roger Federer or Robin Soderling in the semi-final.