The seventh-seeded del Potro, who won the 2009 U.S. Open, reached the semifinals at the event for the second consecutive season.
The 44th-ranked Tursunov was trying to become the first qualifier to reach the tournament's semifinals since David Wheaton in 1994. He won the second set after del Potro double-faulted to set up break point. Del Potro hen volleyed a short Tursunov lob into the net, giving the qualifier a 5-3 lead.
Del Potro responded by breaking Tursunov in the second game of the third set on his way to a 3-0 lead. Another break gave del Potro a 5-1 lead, and he clinched the win with an ace at love.