The hosts totally dominated the first half but could not get the breakthrough they deserved.
Daniel Nardiello smacked a shot against the post after four minutes and, moments later, the same player just failed to reach a great cross from Alex Revell to turn the ball into the net
The visitors survived a strong penalty appeal when Neal Trotman appeared to handle before Tommy Lee produced two great saves to keep Rotherham out, the first from David Noble and the second from Nardiello.
The Spireites' only two chances both fell to Marc Richards with Andy Warrington saving smartly before the striker fired wide after he was picked out by Liam Cooper's free-kick.
Rotherham should have taken the lead in the first minute of the second half when Lee Frecklington sent Revell clear, but he pulled his shot wide of the target. And minutes later Nardiello headed just over the bar.
The breakthrough finally came after 57 minutes from skipper Johnny Mullins. He rose above everyone in a crowded goalmouth to head home Noble's corner.