League Two leaders Chesterfield earned their seventh win in eight games with a narrow victory at 10-man Oxford.
Ritchie Humphreys volleyed in Eoin Doyle's cross to put the Spireites ahead on the half-hour mark.
Oxford defender Andy Whing was shown a straight red for a sliding tackle on Doyle midway through the second-half.
Ryan Clarke made a string of fine saves as Chesterfield dominated, but Dean Smalley almost equalised five minutes from time when his header hit the post.
The win for Chesterfield maintained their four-point lead at the top of the division, while Oxford's first defeat of the season saw them drop out of the top three.
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Chesterfield goalkeeping coach Eric Nixon told BBC Radio Sheffield:
"It was a hard-working performance, but I feel on the day it could have been more goals for us.
"Obviously Oxford are a really good side, but it's nice to come and get three points.
"We've got a great system and the football we play is pleasing on the eye."