Rotherham striker Tom Pope struck late on secure a 1-0 win and shatter Chesterfield with his first goal since August in the local derby at Saltergate.
Pope turned on the edge of the box to drill a low shot into the bottom right corner in the last minute of a game full of effort but low on quality.
There was a lack of composure in the final third in the first half but both teams wasted chances.
After Nicky Law had been foiled by Chesterfield keeper Tommy Lee, Jack Lester fired over before Kevin Ellison sliced well wide.
Rotherham had a great chance to go ahead in the 65th minute when a slip by Aaron Downes let in Adam Le Fondre but the striker fired straight at Lee.
Andy Warrington rescued the visitors in the 73rd minute when he twisted to push over a dipping volley from Downes but Lee was finally beaten by Pope's late strike.
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