Chesterfield lost their unbeaten home league record as Burton celebrated their first away win of the season, triumphing 2-1 at the b2net Stadium.
The League Two leaders recovered from going a goal down but after midfielder Derek Niven was dismissed in the second half, Shaun Harrad came off the bench to win it for the Brewers.
Chesterfield had won seven of their previous eight home games but they were behind after just five minutes when Jack Hunt lost the ball to James Collins who advanced to beat Tommy Lee.
Adam Legzdins made a great one-handed saved to deny Craig Davies but the Burton keeper was beaten a minute before the break when Danny Whitaker turned in a Niven drive.
The visitors had chances to regain the lead early in the second half but Aaron Webster headed straight at Lee and Collins fired over when clear after Lee had kept out a Darren Moore strike.
Chesterfield were reduced to 10 men in the 57th minute when Niven was sent off for a late challenge, and Burton won it eight minutes from the end when Harrard's low shot from the edge of the area found the bottom right corner.
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