The visitors came close to breaking the deadlock in the 11th minute when the ball fell to Takashi Inui, whose shot clipped the post on its way wide.
Alexander Meier should have put his side ahead in the 22nd minute when Kadlec's pass found the striker in space 14 yards from goal, but he fired his effort high and wide.
Frankfurt opened the scoring less than 10 minutes after the restart when Vaclav Kadlec found Meier, whose shot took a big deflection off Ermin Bicakcic before going in.
They doubled this lead 10 minutes later when Stefan Aigner pounced on a defensive error before sliding the ball past the keeper to give his side some breathing space.
Frankfurt were pushing for a third by the end and almost got it when Jan Rosenthal advanced with the ball before shooting just wide.