The Spaniard looked out of sorts as Haas broke him at love for a 3-2 lead in the opening set, and the German broke him again for a 5-2 lead.
Ferrer managed to cut down on his errors in the second set, breaking Haas twice to force a deciding third set.
Ferrer said his service game would be the key against Murray on Sunday.
“I will have to do everything good,” he said. “I will have to improve my first serve, to play obviously with my forehand sure for to beat him.”