Scunthorpe could have also doubled their advantage, with Dagnall, again, going close when he headed Mark Duffy's free-kick narrowly wide of the top-right corner.
But the visitors were playing a full share in the game and almost levelled when Matthew Taylor's goalbound free-kick from long range was deflected wide for a corner.
Muntari had the first decent effort at goal, driving narrowly over with a 25-yard free-kick, while Herman Hreidarsson headed wide from a Kranjcar corner.