Chesterfield's unbeaten record was shattered by neighbours Rotherham after a pulsating derby clash was won thanks to a flash of brilliance from Adam Le Fondre.
After a bright start in which they won three corners in the first 10 minutes, Chesterfield lost the initiative and the home side carved out a hatful of chances, but failed to take any of them.
The Millers' best chance fell to Danny Harrison, who was left with a free header six yards out from Kevin Ellison's cross, but the midfielder somehow headed wide.
And Chesterfield almost capitalised on Rotherham's generosity in front of goal when Mark Allott picked out a peach of a pass for Jack Lester, but he was thwarted by a brilliant save from Andy Warrington.
But nine minutes after the break Rotherham did take the lead with a goal of sheer class, as Le Fondre allowed Johnny Mullins throw in to run on the edge of the box and with everyone expecting a cross, he calmly lobbed the ball into the opposite corner for his ninth goal of the season.
Warrington pulled off two more splendid saves from Dean Morgan and Craig Davis as Chesterfield turned up the heat, but Le Fondre's touch of genius was enough.