Kevin Grosskreutz was the first to threaten for Dortmund as he cut inside from the left after two minutes had been played, though his low shot was saved at the bottom corner of goal.
Lars Stindl thought he had given Hannover the lead as Hummels made a mess of his clearance, only for the player to see his effort crash back off of the Dortmund post.
It was Stindl who troubled the visitors again just before half time, with the midfielder picking the ball up from an acute angle before getting a shot off with his right. However, Roman Weidenfeller did well to get across and make the save.
Hummels gave Dortmund the lead just before half time as he was able to flick home following a delivery from Jonas Hofmann.