Chesterfield missed the chance to move into the League Two play-off places after a 1-1 draw against Colchester.
After Jack Payne found a quick opener for United, Will Grigg was on target for the sixth time in five games for the Spireites, who failed to capitalise on many chances to grab the winner.
Payne comfortably slotted the ball into the corner of the net in the sixth minute following Oscar Thorn's fast ball into the packed penalty area.
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The hosts almost found an equaliser after a long-range free-kick from James Berry rattled the inside of the post and went inches away from rebounding beyond the goal line.
There was much debate in the 64th minute after Grigg seemingly had the final touch after Darren Oldaker fired a stunning volley goalwards and the goal was given.
Chesterfield nearly grabbed three valuable points late in stoppage time when Paddy Madden's close-range effort in the penalty area sailed over the bar.