Leaders Chesterfield have lost in League Two for the first time in seven games.
The Spireites were beaten at Wycombe Wanderers courtesy of a 35th-minute penalty from Max Kretzschmar.
Kretzschmar drilled his spot kick down the middle of the goal after Matt McClure's cross had struck the hand of Spireites captain Ian Evatt.
A frustrated Paul Cook was sent to the stands in first-half stoppage time and the Chesterfield manager's mood did not improve after the break.
Cook briefly thought that his side had drawn level, only for Evatt's back-post header to be ruled out for offside.
Chesterfield remain top of the table because they have a better goal difference than second-placed Scunthorpe United.
However, the Spireites are only three goals clear of Scunthorpe, who thrashed Portsmouth 5-1 today.
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