A goal on the stroke of half time gave Roy McFarland's side the edge as they recovered from a run of three straight defeats.
Kevan Hurst produced a cracking low shot from the edge of the box to beat Gary Montgomery after Paul McLaren had gifted the visitors the free kick when he brought down Jamie O'Hara.
Minutes earlier Rotherham blew a carbon copy chance when John Mullin smashed a free kick over the top after Steve Blatherwick tripped Andy Monkhouse.
Four minutes into the second half the visitors added a second when Derek Niven struck a sweet shot picking his spot with a super side-foot shot from 20 yards.
And on 54 minutes the visitors put the game beyond the home side who have never beaten Chesterfield at Millmoor in eight league attempts since 1979.
It was Mark Allott who grabbed the third pouncing onto a loose ball to volley a 25 yard effort past Gary Montgomery. And on 86 minutes Jamie O'Hara added the fourth with another great strike.
Rotherham had their chances but missed the opportunities. After 36 minutes Steve Blatherwick felled Andy Monkhouse as the winger cut across the edge of the area.
The home side were protesting that Monkhouse was in the area but their claims for a penalty were dismissed and John Mullin hoisted his attempt from the free kick.
But Rotherham failed to produce any meaningful attempts until the visitors had claimed their three goals.
It was 72 minutes before Rotherham opened up the stubborn Chesterfield defence as Will Hoskins burst down the left. He cut back a crisp pass but Paul Shaw hit a tame effort at the keeper. Two minutes later Martin Butler rounded the keeper but hit the post.