The Russian will meet third seed Tomas Berdych for the title. The Czech beat unseeded Austrian Stefan Koubek 7-6 6-2 in the other semi-final.
Tursunov won the first set on a tiebreak after he broke world number seven Robredo in the seven game but was himself broken in the 10th.
The 24-year-old Robredo, who is aiming to qualify for the year-end Masters Cup in Shanghai, discovered his rhythm in the second and bagged it thanks to some explosive returns.
But Tursunov, who last week put Russia in the Davis Cup final after a tough five-set victory over American Andy Roddick, rattled Robredo with his big serves in the decider to wrap up victory in quick time