After a spell of early pressure skipper Pablo Mills fired a shot into a crowded area and when the ball broke to striker Mark Burchill his snapshot was wide of Simon Brown's goal.
Another effort from Dale Tonge was high over the top and Brown held onto another half chance fired in by Micky Cummins.
But Darlington, who defended in numbers, shut out the home side and came up with their own scoring chances before the break.
Jason Kennedy produced a shot that was blocked on the edge of the area after good work by Liam Hatch.
A Franz Burgmeier volley from distance was wide and when the visitors were gifted a free kick on the edge of the area, former Barnsley defender Neil Austin curled his shot over the top.
Darlington went within a whisker of an opener when Hatch charged forward on the break and smashed a powerful effort from 25 yards that beat keeper Andy Warrington but grazed the post.
As Rotherham started the second half in determined mood, Burchill shot over from the edge of the area and Danny Harrison drove over the top.
Rotherham manager Mark Robins switched his strike force bringing on Richie Barker and Reuben Reid for Drewe Broughton and Burchill.
But it was Darlington who made the breakthrough after 61 minutes when Rotherham failed to clear a dangerous ball into the area.
The ball broke to Ricky Ravenhill who clipped a shot from ten yards out to beat Warrington.
Rotherham responded and came close to an equaliser but a shot from sub Mark Hudson was cleared off the line by Austin.