League Two leaders Rochdale crashed to their first defeat in seven games when a second half penalty double by Barry Conlon boosted Chesterfield's promotion hopes in a 2-0 win.
Rochdale had started the game with all the confidence of a team that had won their last three matches and should have scored in the 32nd minute.
Chris Dagnall's low cross was backheeled by Joe Thompson to Jason Kennedy four yards out but his shot hit a defender on the line.
But for all their possession, the visitors had created few chances and they were lucky when former Rochdale winger Adam Rundle miscued from 12 yards in the 51st minute.
Dagnall had a shot saved in the 58th minute but Rundle was denied by a superb reaction save by Frank Fielding at his near post on the hour.
But Fielding was beaten in the 68th minute when Nathan Stanton handled a low cross and Conlon drove in the penalty.
Rochdale almost levelled a minute later but Tommy Lee made a brilliant save to deny Chris O'Grady and Conlon bagged his second spot kick in the 82nd minute when Rory McArdle tripped Ishmel Demontagnac.
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