sebastian kehl scored in extra time to edge borussia dortmund past hoffenheim 3-2 in the german cup quarter-finals .
dortmund had taken an early lead in the 19th minute through neven subotic 's goal before kevin volland equalised for the visitors .
roberto firmino then gave hoffenheim the lead with a superb chipped shot before patrick aubameyang pulled dortmund level .
in extra time , kehl hit a wonderful volleyed effort from outside the box .